Semiconductor device and fabrication method of semiconductor device

ABSTRACT

A semiconductor device including: a first insulator in which an opening is formed; a first conductor positioned in the opening; a first oxide over the first insulator; a second oxide over the first oxide; a third oxide and a fourth oxide over the second oxide; a second conductor over the third oxide and the first conductor; a third conductor over the fourth oxide; a fifth oxide over the second oxide; a second insulator over the fifth oxide; and a fourth conductor positioned over the second insulator and overlapping with the fifth oxide. The fifth oxide is in contact with each of a side surface of the third oxide and a side surface of the fourth oxide. The conductivity of the third oxide is higher than the conductivity of the second oxide. The second conductor is in contact with the top surface of the first conductor.

TECHNICAL FIELD

One embodiment of the present invention relates to a semiconductordevice and a method for fabricating the semiconductor device.Alternatively, one embodiment of the present invention relates to asemiconductor wafer, a module, and an electronic device.

In this specification and the like, a semiconductor device generallymeans a device that can function by utilizing semiconductorcharacteristics. A semiconductor element such as a transistor, asemiconductor circuit, an arithmetic device, and a memory device areeach an embodiment of a semiconductor device. A display device (e.g., aliquid crystal display device and a light-emitting display device), aprojection device, a lighting device, an electro-optical device, a powerstorage device, a memory device, a semiconductor circuit, an imagingdevice, an electronic device, and the like may include a semiconductordevice.

Note that one embodiment of the present invention is not limited to theabove technical field. One embodiment of the invention disclosed in thisspecification and the like relates to an object, a method, or amanufacturing method. Alternatively, one embodiment of the presentinvention relates to a process, a machine, manufacture, or a composition(composition of matter).

BACKGROUND ART

As semiconductor thin films applicable to the transistors, silicon-basedsemiconductor materials have been widely known, but oxide semiconductorshave been attracting attention as alternative materials. Examples ofoxide semiconductors include not only single-component metal oxides,such as indium oxide and zinc oxide, but also multi-component metaloxides.

Among the multi-component metal oxides, in particular, an In—Ga—Zn oxide(hereinafter also referred to as IGZO) has been actively studied.

From the studies on IGZO, in an oxide semiconductor, a CAAC (c-axisaligned crystalline) structure and an ne (nanocrystalline) structure,which are not single crystal nor amorphous, have been found (seeNon-Patent Documents 1 to 3). In Non-Patent Documents 1 and 2, atechnique for fabricating a transistor using an oxide semiconductorhaving the CAAC structure is disclosed. Moreover, Non-Patent Documents 4and 5 disclose that a fine crystal is included even in an oxidesemiconductor which has lower crystallinity than an oxide semiconductorhaving the CAAC structure or the nc structure.

In addition, a transistor which includes IGZO as an active layer has anextremely low off-state current (see Non-Patent Document 6), and an LSIand a display utilizing the transistor characteristics have beenreported (see Non-Patent Documents 7 and 8).

REFERENCE Non-Patent Document

-   [Non-Patent Document 1] S. Yamazaki et al., “SID Symposium Digest of    Technical Papers”, 2012, volume 43, issue 1, p. 183-186-   [Non-Patent Document 2] S. Yamazaki et al., “Japanese Journal of    Applied Physics”, 2014, volume 53, Number 4S, p. 04ED18-1-04ED18-10-   [Non-Patent Document 3] S. Ito et al., “The Proceedings of AM-FPD′13    Digest of Technical Papers”, 2013, p. 151-154-   [Non-Patent Document 4] S. Yamazaki et al., “ECS Journal of Solid    State Science and Technology”, 2014, volume 3, issue 9, p.    Q3012-Q3022-   [Non-Patent Document 5] S. Yamazaki, “ECS Transactions”, 2014,    volume 64, issue 10, p. 155-164-   [Non-Patent Document 6] K. Kato et al., “Japanese Journal of Applied    Physics”, 2012, volume 51, p. 021201-1-021201-7-   [Non-Patent Document 7] S. Matsuda et al., “2015 Symposium on VLSI    Technology Digest of Technical Papers”, 2015, p. T216-T217-   [Non-Patent Document 8] S. Amano et al., “SID Symposium Digest of    Technical Papers”, 2010, volume 41, issue 1, p. 626-629

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Another object of one embodiment of the present invention is to providea semiconductor device that can be miniaturized or highly integrated.Another object of one embodiment of the present invention is to providea semiconductor device with excellent electrical characteristics.Another object of one embodiment of the present invention is to providea semiconductor device with high on-state current. Another object of oneembodiment of the present invention is to provide a semiconductor devicewith excellent frequency characteristics. Another object of oneembodiment of the present invention is to provide a highly reliablesemiconductor device. Another object of one embodiment of the presentinvention is to provide a semiconductor device with high productivity.

An object of one embodiment of the present invention is to provide asemiconductor device capable of retaining data for a long time. Anobject of one embodiment of the present invention is to provide asemiconductor device capable of high-speed data writing. An object ofone embodiment of the present invention is to provide a semiconductordevice with high design flexibility. An object of one embodiment of thepresent invention is to provide a semiconductor device capable ofreducing power consumption. An object of one embodiment of the presentinvention is to provide a novel semiconductor device.

Note that the descriptions of these objects do not disturb the existenceof other objects. One embodiment of the present invention does not haveto achieve all the objects. Other objects will be apparent from and canbe derived from the description of the specification, the drawings, theclaims, and the like.

Means for Solving the Problems

One embodiment of the present invention is a semiconductor deviceincluding: a first insulator in which an opening is formed; a firstconductor positioned in the opening; a first oxide over the firstinsulator; a second oxide over the first oxide; a third oxide and afourth oxide over the second oxide; a second conductor over the thirdoxide and the first conductor; a third conductor over the fourth oxide;a fifth oxide over the second oxide; a second insulator over the fifthoxide; and a fourth conductor positioned over the second insulator andoverlapping with the fifth oxide. The fifth oxide is in contact witheach of the side surface of the third oxide and the side surface of thefourth oxide. The conductivity of the third oxide is higher than theconductivity of the second oxide. The conductivity of the fourth oxideis higher than the conductivity of the second oxide. The secondconductor is in contact with the top surface of the first conductor.

Another embodiment of the present invention is a semiconductor deviceincluding: a first insulator in which an opening is formed; a firstconductor positioned in the opening; a first oxide over the firstinsulator; a second oxide over the first oxide; a third oxide and afourth oxide over the second oxide; a second conductor over the thirdoxide and the first conductor; a third conductor over the fourth oxide;a fifth oxide over the second oxide; a second insulator over the fifthoxide; and a fourth conductor positioned over the second insulator andoverlapping with the fifth oxide. The third oxide includes a firstregion that does not overlap with the second conductor. The fourth oxideincludes a second region that does not overlap with the third conductor.The fifth oxide is in contact with the top surface of the first regionand the top surface of the second region. The conductivity of the thirdoxide is higher than the conductivity of the second oxide. Theconductivity of the fourth oxide is higher than the conductivity of thesecond oxide. The second conductor is in contact with the top surface ofthe first conductor.

The semiconductor device may further include a fifth conductor incontact with the top surface of the second conductor. The fifthconductor may overlap with at least part of the first conductor.

Another embodiment of the present invention is a semiconductor deviceincluding: a first to a third insulator; a first to a sixth conductor; afirst to a fifth oxide; a capacitor; and a transistor. The capacitorincludes, the fifth conductor, the third insulator over the fifthconductor, the sixth conductor over the third insulator. The transistorincludes the first insulator in which an opening is formed, the firstconductor positioned in the opening, the first oxide over the firstinsulator, the second oxide over the first oxide, the third oxide andthe fourth oxide over the second oxide, the second conductor over thethird oxide and the first conductor, the third conductor over the fourthoxide, the fifth oxide over the second oxide, the second insulator overthe fifth oxide, and the fourth conductor positioned over the secondinsulator and overlapping with the fifth oxide. The fifth oxide is incontact with each of the side surface of the third oxide and the sidesurface of the fourth oxide. The conductivity of the third oxide ishigher than the conductivity of the second oxide. The conductivity ofthe fourth oxide is higher than the conductivity of the second oxide.The second conductor is in contact with the top surface of the firstconductor.

Another embodiment of the present invention is a semiconductor deviceincluding: a first to a third insulator; a first to a sixth conductor; afirst to a fifth oxide; a capacitor; and a transistor. The capacitorincludes the fifth conductor, the third insulator over the fifthconductor, and the sixth conductor over the third insulator. Thetransistor includes the first insulator in which an opening is formed,the first conductor positioned in the opening, the first oxide over thefirst insulator, the second oxide over the first oxide, the third oxideand the fourth oxide over the second oxide, the second conductor overthe third oxide and the first conductor, the third conductor over thefourth oxide, the fifth oxide over the second oxide, the secondinsulator over the fifth oxide, and the fourth conductor positioned overthe second insulator and overlapping with the fifth oxide. The thirdoxide includes a first region that does not overlap with the secondconductor. The fourth oxide includes a second region that does notoverlap with the third conductor. The fifth oxide is in contact witheach of the top surface of the first region and the top surface of thesecond region. The conductivity of the third oxide is higher than theconductivity of the second oxide. The conductivity of the fourth oxideis higher than the conductivity of the second oxide. The secondconductor is in contact with the top surface of the first conductor.

It is preferable that the capacitor be formed below the transistor andthe first conductor be electrically connected to the sixth conductor.

A fourth insulator in which an opening is formed may be provided belowthe first insulator, and at least part of the fifth conductor, the thirdinsulator, and the sixth conductor may be positioned in the opening ofthe fourth insulator.

Another embodiment of the present invention is a semiconductor deviceincluding: a first to a fourth insulator; a first to a seventhconductor; a first to a fifth oxide; a capacitor; a first transistor,and a second transistor. The capacitor includes the fifth conductor, thethird insulator over the fifth conductor, and the sixth conductor overthe third insulator. The first transistor includes the first insulatorin which an opening is formed, the first conductor positioned in theopening, the first oxide over the first insulator, the second oxide overthe first oxide, the third oxide and the fourth oxide over the secondoxide, the second conductor over the third oxide and the firstconductor, the third conductor over the fourth oxide, the fifth oxideover the second oxide, the second insulator over the fifth oxide, andthe fourth conductor positioned over the second insulator andoverlapping with the fifth oxide. The fifth oxide is in contact witheach of the side surface of the third oxide and the side surface of thefourth oxide. The conductivity of the third oxide is higher than theconductivity of the second oxide. The conductivity of the fourth oxideis higher than the conductivity of the second oxide. The secondconductor is in contact with the top surface of the first conductor. Thesecond transistor includes the fourth insulator over a silicon substrateand the seventh conductor over the fourth insulator.

Another embodiment of the present invention is a semiconductor deviceincluding: a first to a fourth insulator; a first to a seventhconductor; a first to a fifth oxide; a capacitor; a first transistor,and a second transistor. The capacitor includes the fifth conductor, thethird insulator over the fifth conductor, and the sixth conductor overthe third insulator. The first transistor includes the first insulatorin which an opening is formed, the first conductor positioned in theopening, the first oxide over the first insulator, the second oxide overthe first oxide, the third oxide and the fourth oxide over the secondoxide, the second conductor over the third oxide and the firstconductor, the third conductor over the fourth oxide, the fifth oxideover the second oxide, the second insulator over the fifth oxide, andthe fourth conductor positioned over the second insulator andoverlapping with the fifth oxide. The third oxide includes a firstregion that does not overlap with the second conductor. The fourth oxideincludes a second region that does not overlap with the third conductor.The fifth oxide is in contact with each of the top surface of the firstregion and the top surface of the second region. The conductivity of thethird oxide is higher than the conductivity of the second oxide. Theconductivity of the fourth oxide is higher than the conductivity of thesecond oxide. The second conductor is in contact with the top surface ofthe first conductor. The second transistor includes the fourth insulatorover a silicon substrate and the seventh conductor over the fourthinsulator.

Furthermore, the first transistor may include an eighth conductor incontact with the top surface of the second conductor. The capacitor maybe formed over the first transistor. The eighth conductor may beelectrically connected to the fifth conductor. The second transistor maybe formed below the first transistor. The first conductor may beelectrically connected to the seventh conductor.

Furthermore, a fifth insulator in which an opening is formed may beprovided over the eighth conductor. At least part of the fifthconductor, the third insulator and the sixth conductor may be positionedin the opening of the fifth insulator.

The third oxide and the fourth oxide each preferably include zinc.

The thickness of the third oxide and the fourth oxide is preferably eachlarger than or equal to 1 nm and smaller than or equal to 10 nm.

The third oxide and the fourth oxide each preferably has crystallinity.

The second oxide preferably includes In, an element M (M is Al, Ga, Y,or Sn), and Zn.

Effect of the Invention

According to one embodiment of the present invention, a semiconductordevice that can be miniaturized or highly integrated can be provided.Alternatively, according to one embodiment of the present invention, asemiconductor device with excellent electrical characteristics can beprovided. Alternatively, according to one embodiment of the presentinvention, a semiconductor device with high on-state current can beprovided. Alternatively, according to one embodiment of the presentinvention, a semiconductor device with excellent frequencycharacteristics can be provided. Alternatively, according to oneembodiment of the present invention, a highly reliable semiconductordevice can be provided. Alternatively, according to one embodiment ofthe present invention, a semiconductor device with high productivity canbe provided.

Alternatively, it is possible to provide a semiconductor device capableof retaining data for a long time. Alternatively, it is possible toprovide a semiconductor device capable of high-speed data writing.Alternatively, it is possible to provide a semiconductor device withhigh design flexibility. Alternatively, it is possible to provide asemiconductor device capable of reducing power consumption.Alternatively, it is possible to provide a novel semiconductor device.

Note that the descriptions of the effects do not disturb the existenceof other effects. One embodiment of the present invention does not haveto have all of these effects. Effects other than these will be apparentfrom the description of the specification, the drawings, the claims, andthe like and effects other than these can be derived from thedescription of the specification, the drawings, the claims, and thelike.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (A)-(C) A top view and cross-sectional views of a semiconductordevice of one embodiment of the present invention.

FIG. 2 (A)-(C) A top view and cross-sectional views of a semiconductordevice of one embodiment of the present invention.

FIG. 3 (A)(B) Cross-sectional views of a semiconductor device of oneembodiment of the present invention.

FIG. 4 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 5 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 6 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 7 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 8 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 9 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 10 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 11 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 12 A diagram illustrating an energy band structure of an oxidesemiconductor.

FIG. 13 (A)(B) A top view and a cross-sectional view of a semiconductordevice of one embodiment of the present invention.

FIG. 14 (A)(B) A top view and a cross-sectional view of a semiconductordevice of one embodiment of the present invention.

FIG. 15 (A)(B) A top view and a cross-sectional view of a semiconductordevice of one embodiment of the present invention.

FIG. 16 (A)-(C) A top view and cross-sectional views of a semiconductordevice of one embodiment of the present invention.

FIG. 17 A cross-sectional view of a semiconductor device of oneembodiment of the present invention.

FIG. 18 (A), (B) Cross-sectional views of a semiconductor device of oneembodiment of the present invention.

FIG. 19 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 20 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 21 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 22 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 23 (A)-(C) A top view and cross-sectional views illustrating amethod for fabricating a semiconductor device of one embodiment of thepresent invention.

FIG. 24 A cross-sectional view illustrating a structure of a memorydevice of one embodiment of the present invention.

FIG. 25 A cross-sectional view illustrating a structure of a memorydevice of one embodiment of the present invention.

FIG. 26 A cross-sectional view illustrating a structure of a memorydevice of one embodiment of the present invention.

FIG. 27 (A)(B) Block diagrams illustrating structure examples of amemory device of one embodiment of the present invention.

FIG. 28 (A)-(H) Circuit diagrams each illustrating a structure exampleof a memory device of one embodiment of the present invention.

FIG. 29 (A) (B) Schematic views of a semiconductor device of oneembodiment of the present invention.

FIG. 30 (A)-(E) Schematic views of memory devices of one embodiment ofthe present invention.

FIG. 31 A diagram describing a product image applicable to asemiconductor device of one embodiment of the present invention.

FIG. 32 (A)-(F) Diagrams illustrating electronic devices of oneembodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described below with reference to the drawings. Notethat the embodiments can be implemented with many different modes, andit will be readily understood by those skilled in the art that modes anddetails thereof can be changed in various ways without departing fromthe spirit and scope thereof. Therefore, the present invention shouldnot be construed as being limited to the description of embodimentsbelow.

In addition, in the drawings, the size, the layer thickness, or theregion is exaggerated for clarity in some cases. Therefore, they are notlimited to the illustrated scale. Note that the drawings schematicallyillustrate ideal examples, and embodiments of the present invention arenot limited to shapes, values, and the like shown in the drawings. Forexample, in an actual manufacturing process, a layer, a resist mask, orthe like might be unintentionally reduced in size by treatment such asetching, which might be omitted for easy understanding. Furthermore, inthe drawings, the same reference numerals are used in common for thesame portions or portions having similar functions in differentdrawings, and repeated description thereof is omitted in some cases. Thesame hatching pattern is used for portions having similar functions, andthe portions are not denoted by specific reference numerals in somecases.

In a top view (also referred to as a plan view), a perspective view, orthe like, particularly, some components might not be illustrated foreasy understanding of the invention. In addition, some hidden lines andthe like might not be shown.

Note that the ordinal numbers such as “first” and “second” in thisspecification and the like are used for convenience and do not denotethe order of steps or the stacking order of layers. Therefore, forexample, the term “first” can be replaced with the term “second”,“third”, or the like as appropriate. In addition, the ordinal numbers inthis specification and the like are not necessarily the same as thosewhich specify one embodiment of the present invention.

In addition, in this specification and the like, terms for describingarrangement, such as “over” and “below”, are used for convenience todescribe the positional relationship between components with referenceto drawings. Furthermore, the positional relationship between componentsis changed as appropriate in accordance with a direction in which thecomponents are described. Thus, terms for the description are notlimited to terms used in the specification, and description can be madeappropriately depending on the situation.

When this specification and the like explicitly state that X and Y areconnected, for example, the case where X and Y are electricallyconnected, the case where X and Y are functionally connected, and thecase where X and Y are directly connected are regarded as beingdisclosed in this specification and the like. Accordingly, without beinglimited to a predetermined connection relationship, for example, aconnection relationship shown in drawings or text, a connectionrelationship other than a connection relationship shown in drawings ortext is regarded as being disclosed in the drawings or the text.

Here, X and Y each denote an object (e.g., a device, an element, acircuit, a wiring, an electrode, a terminal, a conductive film, or alayer).

Furthermore, functions of a source and a drain might be interchangedwith each other when a transistor of opposite polarity is employed orwhen the direction of current is changed in circuit operation, forexample. Therefore, the terms “source” and “drain” can sometimes beinterchanged with each other in this specification and the like.

Note that in this specification and the like, depending on thetransistor structure, a channel width in a region where a channel isactually formed (hereinafter also referred to as an effective channelwidth) is different from a channel width shown in a top view of atransistor (hereinafter also referred to as an apparent channel width)in some cases. For example, in a transistor whose gate electrode coversthe side surface of a semiconductor, the effective channel width islarger than the apparent channel width, and its influence cannot beignored in some cases. For example, in a miniaturized transistor whosegate electrode covers a semiconductor, the proportion of a channelformation region formed in a side surface of the semiconductor isincreased in some cases. In that case, effective channel width isgreater than apparent channel width.

In such a case, effective channel width is sometimes difficult toestimate by actual measurement. For example, estimation of effectivechannel width from a design value requires assumption that the shape ofa semiconductor is known. Accordingly, in the case where the shape of asemiconductor is not known accurately, it is difficult to measureeffective channel width accurately.

Furthermore, in this specification, the simple term “channel width”refers to apparent channel width in some cases. Alternatively, in thisspecification, the simple term “channel width” refers to effectivechannel width in some cases. Note that values of channel length, channelwidth, effective channel width, apparent channel width, and the like canbe determined, for example, by analyzing a cross-sectional TEM image andthe like.

Note that impurities in a semiconductor refer to, for example, elementsother than the main components of a semiconductor. For example, anelement with a concentration lower than 0.1 atomic % can be regarded asan impurity. When an impurity is contained, for example, DOS (Density ofStates) in a semiconductor might be increased or crystallinity might bedecreased. In the case where the semiconductor is an oxidesemiconductor, examples of an impurity that changes characteristics ofthe semiconductor include Group 1 elements, Group 2 elements, Group 13elements, Group 14 elements, Group 15 elements, and transition metalsother than the main components of the oxide semiconductor; hydrogen,lithium, sodium, silicon, boron, phosphorus, carbon, and nitrogen aregiven as examples. In the case of an oxide semiconductor, water alsoserves as an impurity in some cases. Also in the case of an oxidesemiconductor, oxygen vacancies are formed by the mixing of impurities,for example. Furthermore, when the semiconductor is silicon, examples ofthe impurity that changes characteristics of the semiconductor includeoxygen, Group 1 elements except for hydrogen, Group 2 elements, Group 13elements, and Group 15 elements.

Note that in this specification and the like, silicon oxynitride is amaterial that contains more oxygen than nitrogen in its composition.Moreover, silicon nitride oxide is a material that contains morenitrogen than oxygen in its composition.

In addition, in this specification and the like, the term “insulator”can be replaced with an insulating film or an insulating layer.Furthermore, the term “conductor” can be replaced with a conductive filmor a conductive layer. Moreover, the term “semiconductor” can bereplaced with a semiconductor film or a semiconductor layer.

In addition, in this specification and the like, “parallel” indicates astate where two straight lines are placed at an angle greater than orequal to −10° and less than or equal to 10°. Accordingly, the case wherethe angle is greater than or equal to −5° and less than or equal to 5°is also included. Furthermore, “substantially parallel” indicates astate where two straight lines are placed at an angle greater than orequal to −30° and less than or equal to 30°. Moreover, “perpendicular”indicates a state where two straight lines are placed at an anglegreater than or equal to 80° and less than or equal to 100°.Accordingly, the case where the angle is greater than or equal to 85°and less than or equal to 95° is also included. Moreover, “substantiallyperpendicular” indicates a state where two straight lines are placed atan angle greater than or equal to 60° and less than or equal to 120°.

Note that in this specification, a barrier film means a film having afunction of inhibiting the transmission of oxygen and impurities such aswater and hydrogen; in the case where the barrier film has conductivity,the barrier film is referred to as a conductive barrier film in somecases.

In this specification and the like, a metal oxide is an oxide of metalin a broad sense. Metal oxides are classified into an oxide insulator,an oxide conductor (including a transparent oxide conductor), an oxidesemiconductor (also simply referred to as an OS), and the like. Forexample, in the case where a metal oxide is used in a semiconductorlayer of a transistor, the metal oxide is referred to as an oxidesemiconductor in some cases. That is, in the case where an OS FET or anOS transistor is stated, the OS FET or the OS transistor can also bereferred to as a transistor including an oxide or an oxidesemiconductor.

In addition, in this specification and the like, “normally off” meansthat current per micrometer of channel width flowing through atransistor when a potential is not applied to a gate or a groundpotential is applied to the gate is lower than or equal to 1×10⁻²⁰ A atroom temperature, lower than or equal to 1×10⁻¹⁸ A at 85° C., or lowerthan or equal to 1×10⁶ A at 125° C.

Embodiment 1

An example of a semiconductor device including the transistor 200 of oneembodiment of the present invention is described below.

<Structure Example of Semiconductor Device>

FIG. 1(A), FIG. 1(B), and FIG. 1(C) are a top view and cross-sectionalviews of a transistor 200 according to one embodiment of the presentinvention and the periphery of the transistor 200.

FIG. 1(A) is a top view of a semiconductor device including thetransistor 200. FIG. 1(B) and FIG. 1(C) are cross-sectional views of thesemiconductor device. Here, FIG. 1(B) is a cross-sectional view of aportion indicated by a dashed-dotted line A1-A2 in FIG. 1(A), and is across-sectional view in the channel length direction of the transistor200. In addition, FIG. 1(C) is a cross-sectional view of a portionindicated by a dashed-dotted line A3-A4 in FIG. 1(A), and is across-sectional view in the channel width direction of the transistor200. Note that for clarity of the drawing, some components are notillustrated in the top view of FIG. 1(A).

The semiconductor device of one embodiment of the present inventionincludes an insulator 214 over a substrate (not illustrated), thetransistor 200 over the insulator 214, an insulator 280 over thetransistor 200, an insulator 282 over the insulator 280, an insulator274 over the insulator 282, and an insulator 281 over the insulator 274.The insulator 214, insulator 280, insulator 282, the insulator 274, andthe insulator 281 function as interlayer films. A conductor 247 thatfunctions as a plug and is electrically connected to the transistor 200is provided. A conductor 240 (a conductor 240 a and a conductor 240 b)that functions as a plug and is electrically connected to the transistor200 is also provided. Note that an insulator 241 (an insulator 241 a andan insulator 241 b) is provided in contact with a side surface of theconductor 240 functioning as a plug. A conductor 246 (a conductor 246 aand a conductor 246 b) electrically connected to the conductor 240 andfunctioning as a wiring is provided over the insulator 281 and theconductor 240.

The insulator 241 a is provided in contact with the inner wall of anopening in an insulator 272, an insulator 273, the insulator 280,insulator 282, the insulator 274, and the insulator 281, a firstconductor of the conductor 240 a is provided in contact with the sidesurface of the insulator 241 a, and a second conductor of the conductor240 a is provided on the inner side thereof. The insulator 241 b isprovided in contact with the inner wall of an opening in the insulator272, the insulator 273, the insulator 280, the insulator 282, theinsulator 274, and the insulator 281, a first conductor of the conductor240 b is provided in contact with the side surface of the insulator 241b, and a second conductor of the conductor 240 b is provided on theinner side thereof. Here, the level of a top surface of the conductor240 and the level of a top surface of the insulator 281 can besubstantially the same. Although the structure in which the firstconductor of the conductor 240 and the second conductor of the conductor240 are stacked is described in this embodiment, the present inventionis not limited thereto. For example, the conductor 240 may be providedas a single layer or to have a stacked-layer structure of three or morelayers. In contact with the inner wall of an opening formed in aninsulator 214, an insulator 216, an insulator 222, and an insulator 224,a first conductor of the conductor 247 is provided, and a secondconductor of the conductor 247 is further provided on the inner side.Although the structure in which the first conductor of the conductor 247and the second conductor of the conductor 247 are stacked is described,the present invention is not limited thereto. For example, the conductor247 may be provided as a single layer or to have a stacked-layerstructure of three or more layers. In the case where a structure bodyhas a stacked-layer structure, layers may be distinguished by ordinalnumbers corresponding to the formation order.

[Transistor 200]

As shown in FIG. 1, the transistor 200 includes the insulator 216 overthe insulator 214; a conductor 205 (a conductor 205 a and a conductor205 b) positioned so as to be embedded in the insulator 216; theinsulator 222 over the insulator 216 and the conductor 205; theinsulator 224 over the insulator 222; an oxide 230 a over the insulator224; an oxide 230 b over the oxide 230 a; an oxide 243 a and an oxide243 b over the oxide 230 b; a conductor 242 a in contact with part ofthe top surface of the insulator 224, the side surface of the oxide 230a, the side surface of the oxide 230 b, the side surface of the oxide243 a, and the top surface of the oxide 243 a; a conductor 242 b incontact with part of the top surface of the insulator 224, the sidesurface of the oxide 230 a, the side surface of the oxide 230 b, theside surface of the oxide 243 b, and the top surface of the oxide 243 b;an oxide 230 c over the oxide 230 b; an insulator 250 over the oxide 230c; a conductor 260 (a conductor 260 a and a conductor 260 b) positionedover the insulator 250 and overlapping with the oxide 230 c; theinsulator 272 in contact with part of the top surface of the insulator224, the side surface of the conductor 242 a, the top surface of theconductor 242 a, the side surface of the conductor 242 b, and the topsurface of the conductor 242 b; and the insulator 273 over the insulator272. The oxide 230 c is in contact with each of the side surface of theoxide 243 a and the side surface of the oxide 243 b. The conductor 260includes the conductor 260 a and the conductor 260 b and the conductor260 a is positioned to cover the bottom surface and the side surface ofthe conductor 260 b. Here, as illustrated in FIG. 1(B), the top surfaceof the conductor 260 is positioned to be substantially aligned with thetop surface of the insulator 250 and the top surface of the oxide 230 c.The insulator 282 is in contact with each of the top surfaces of theconductor 260, the oxide 230 c, the insulator 250, and the insulator280.

An opening is formed in the insulator 214, the insulator 216, theinsulator 222, and the insulator 224, and the conductor 247 ispositioned in the opening. It is preferable that at least part of thetop surface of the conductor 247 be exposed from the insulator 224, andthe top surface of the conductor 247 be substantially aligned with thetop surface of the insulator 224. A structure may be employed where theconductor 247 does not overlap with the oxide 230 a and the oxide 230 b.

Here, the conductor 247 is electrically connected to a circuit elementsuch as a switch, a transistor, a capacitor, an inductor a resistor, anda diode, a wiring, an electrode, or a terminal which are provided in alower layer of the insulator 214. For example, a structure may beemployed where the conductor 247 is electrically connected to a gate ofa transistor provided below the insulator 214. Alternatively, astructure may be employed where the conductor 247 is electricallyconnected to one of electrodes of a capacitor provided below theinsulator 214, for example.

The conductor 242 b is provided over the oxide 243 b and the conductor247. The conductor 242 b is in contact with at least part of the topsurface of the conductor 247. By connecting the conductor 242 b and theconductor 247 in such a manner, electrical resistance between theconductor 247 and a source or a drain of the transistor 200 can bereduced. Furthermore, by not overlapping the conductor 247 with theoxide 230 a and the oxide 230 b, and providing the conductor 242 b tocover the top surface of the conductor 247, electrical resistancebetween the conductor 247 and the source or the drain of the transistor200 can be further reduced.

With such a structure, frequency characteristics of a semiconductordevice including the transistor 200 can be improved and favorableelectric characteristics can be achieved.

It is preferable that, at least part of a circuit element such as aswitch, a transistor, a capacitor, an inductor, a resistor, or a diode,a wiring, an electrode, or a terminal which is electrically connected tothe conductor 247 overlaps with the oxide 230. This can reduce the areaoccupied by the transistor 200, the above-mentioned circuit element, thewiring, the electrode, or the terminal in a top view, so that thesemiconductor device of this embodiment can achieve miniaturization orhigher integration.

Note that the conductor 242 b is provided to be in contact with the sidesurface of the oxide 243 b, the side surface of the oxide 230 a, and theside surface of the oxide 230 b in some cases.

Although the conductor 247 is provided below the conductor 242 b inFIGS. 1(A) and 1(B), the semiconductor device described in thisembodiment is not limited thereto. For example, the conductor 247 may beprovided below the conductor 242 a or the conductor 247 may be providedbelow both of the conductor 242 a and the conductor 242 b.

It is preferable that the insulator 222, the insulator 272, theinsulator 273, and the insulator 282 have a function of inhibitingdiffusion of at least one of hydrogen (e.g., a hydrogen atom, a hydrogenmolecule, and the like). In addition, it is preferable that theinsulator 222, the insulator 272, the insulator 273, and the insulator282 have a function of inhibiting diffusion of oxygen (e.g., at leastone of an oxygen atom, an oxygen molecule, and the like). For example,preferably, the insulator 222, the insulator 272, the insulator 273, andthe insulator 282 each have a lower permeability of one or both ofoxygen and hydrogen than the insulator 224. Preferably, the insulator222, the insulator 272, the insulator 273, and the insulator 282 eachhave a lower permeability of one or both of oxygen and hydrogen than theinsulator 250. Preferably, the insulator 222, the insulator 272, theinsulator 273, and the insulator 282 each have a lower permeability ofone or both of oxygen and hydrogen than the insulator 280.

As illustrated in FIG. 1(B), the insulator 272 is preferably in contactwith the top surface and side surface of the conductor 242 a, the topsurface and side surface of the conductor 242 b, and the top surface ofthe insulator 224. The insulator 273 is preferably provided over and incontact with the insulator 272. Thus, the insulator 280 is isolated fromthe insulator 224, and the oxide 230 by the insulator 272 and theinsulator 273.

The oxide 230 preferably includes the oxide 230 a over the insulator224, the oxide 230 b over the oxide 230 a, and the oxide 230 c which ispositioned over the oxide 230 b and at least partly in contact with thetop surface of the oxide 230 b.

The transistor 200 has, in the region where a channel is formed(hereinafter also referred to as a channel formation region) and itsvicinity, a structure in which three layers of the oxide 230 a, theoxide 230 b, and the oxide 230 c are stacked; however, the presentinvention is not limited thereto. For example, a single layer of theoxide 230 b, a two-layer structure of the oxide 230 b and the oxide 230a, a two-layer structure of the oxide 230 b and the oxide 230 c, or astacked-layer structure of four or more layers may be provided. Althoughthe conductor 260 is shown to have a stacked-layer structure of twolayers in the transistor 200, the present invention is not limitedthereto. For example, the conductor 260 may have a single-layerstructure or a stacked-layer structure of three or more layers.

Here, the conductor 260 functions as a gate electrode of the transistor,and the conductor 242 a and the conductor 242 b function as a sourceelectrode and a drain electrode. In the transistor 200, the conductor260 functioning as a gate electrode is formed in a self-aligned mannerto fill an opening formed by the insulator 280 and the like. Theformation of the conductor 260 in this manner allows the conductor 260to be positioned certainly in the region between the conductor 242 a andthe conductor 242 b without alignment.

In the transistor 200, as the oxide 230 (the oxide 230 a, the oxide 230b, and the oxide 230 c), which includes a channel formation region, ametal oxide functioning as an oxide semiconductor (hereinafter alsoreferred to as an oxide semiconductor) is preferably used.

The transistor 200 using an oxide semiconductor in a channel formationregion has an extremely low leakage current (off-state current) in anon-conduction state; thus, a semiconductor device with low powerconsumption can be provided. An oxide semiconductor can be deposited bya sputtering method or the like, and thus can be used for the transistor200 included in a highly integrated semiconductor device.

For example, as the oxide 230, a metal oxide such as an In-M-Zn oxide(the element M is one kind or a plurality of kinds selected fromaluminum, gallium, yttrium, tin, copper, vanadium, beryllium, boron,titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum,cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the like)is preferably used. In particular, aluminum, gallium, yttrium, or tin ispreferably used for the element M. Furthermore, as the oxide 230, anIn—Ga oxide or an In—Zn oxide may be used.

The electrical characteristics of a transistor using an oxidesemiconductor tend to have variations when impurities and oxygenvacancies exist in the channel formation region of the oxidesemiconductor, and the reliability decreases in some cases. Moreover, ifthe region of the oxide semiconductor where a channel is formed includesoxygen vacancies, the transistor tends to have normally-oncharacteristics. Therefore oxygen vacancies in the region where achannel is formed are preferably reduced as much as possible. Forexample, oxygen is preferably supplied to the oxide 230 through theinsulator 250 or the like to fill the oxygen vacancies. Thus, atransistor that has stable electrical characteristics with a smallvariation in electrical characteristics and improved reliability can beprovided.

As illustrated in FIG. 1(B), in the transistor 200, an oxide 243 (theoxide 243 a and the oxide 243 b) is positioned between the top surfaceof the oxide 230 b and a bottom surface of a conductor 242 (theconductor 242 a, and the conductor 242 b). In this structure, largeparts of the conductor 242 and the oxide 230 are not in contact; thus,absorption of oxygen in the oxide 230 by the conductor 242 can bereduced. That is, inhibiting oxidization of the conductor 242 caninhibit the decrease in conductivity of the conductor 242. Accordingly,the oxide 243 preferably has a function of inhibiting oxidization of theconductor 242.

The oxide 243 preferably has conductivity. When the oxide 243, which hasconductivity, is provided between the conductor 242 that functions as asource electrode or a drain electrode, and the oxide 230 b, theelectrical resistance between the conductor 242 and the oxide 230 b canbe reduced, which is preferable. Such a structure improves theelectrical characteristics and reliability of the transistor 200. Notethat the oxide 243 may have a crystal structure.

As the oxide 243, an oxide containing zinc can be used. For example,zinc oxide, gallium zinc oxide, indium zinc oxide, or indium galliumzinc oxide can be used. Alternatively, indium oxide or indium tin oxidemay be used. The oxide 243 is preferably a metal oxide having a highbond energy between a metal atom and an oxygen atom. The conductivity ofthe oxide 243 is preferably higher than the conductivity of the oxide230 (the oxide 230 a, the oxide 230 b, and the oxide 230 c). Thethickness of the oxide 243 is preferably larger than or equal to 1 nmand smaller than or equal to 10 nm, and more preferably, equal to orlarger than 1 nm and smaller than or equal to 5 nm. The oxide 243preferably has crystallinity. In the case where the oxide 243 hascrystallinity release of oxygen from the oxide 230 can be favorablysuppressed. For example, when the oxide 243 has a hexagonal crystalstructure, release of oxygen from the oxide 230 can sometimes beinhibited.

As shown in FIGS. 1(B) and 1(C), the transistor 200 of one embodiment ofthe present invention has a structure in which the insulator 282 and theinsulator 250 are directly in contact with each other. With such astructure, oxygen contained in the insulator 280 is less likely to beabsorbed into the conductor 260. Therefore, oxygen contained in theinsulator 280 can be injected into the oxide 230 a and the oxide 230 befficiently through the oxide 230 c; hence, oxygen vacancies in theoxide 230 a and the oxide 230 b can be reduced and the electriccharacteristics and the reliability of the transistor 200 can beimproved. In addition, the mixing of impurities such as hydrogencontained in the insulator 280 into the insulator 250 can be suppressed,which can inhibit the adverse effects on the electrical characteristicsand the reliability of the transistor 200. For the insulator 282,silicon nitride, silicon nitride oxide, aluminum oxide, or hafnium oxidecan be used. For the insulator 282, it is favorable to use siliconnitride. The silicon nitride can favorably block an impurity (e.g.,hydrogen or water) from the outside.

The insulator 272 and the insulator 273 preferably have a function ofinhibiting the transmission of oxygen and impurities such as hydrogenand water.

FIG. 3(A) is a cross-sectional view of a portion indicated by adashed-dotted line A5-A6 in FIG. 1(A), and is also a cross-sectionalview in the channel width direction of one of a source region and adrain region of the transistor 200. As illustrated in FIG. 3(A), astructure is employed in which the top surface of the conductor 242 band the side surface of the conductor 242 b are covered with theinsulator 272 and the insulator 273; thus, oxygen and impurities such ashydrogen and water can be inhibited from being diffused into theconductor 242 b from the side surface direction of the conductor 242 band the top surface direction of the conductor 242 b. Hence, diffusionof oxygen from the periphery of the conductor 242 b into the conductor242 b can be inhibited, whereby the oxidation of the conductor 242 b canbe inhibited. Note that a similar effect can also be obtained with theconductor 242 a. Impurities such as hydrogen and water can be inhibitedfrom being diffused into the oxide 230 a and the oxide 230 b from theside surface direction of the oxide 230 a and the side surface directionof the oxide 230 b. For the insulator 272, a silicon oxide film, asilicon nitride film, or a silicon nitride oxide film can be used, forexample. For the insulator 273, aluminum oxide or hafnium oxide can beused, for example.

FIG. 3(B) is a cross-sectional view of a portion indicated by adashed-dotted line A7-A8 in FIG. 1(A), which corresponds to across-sectional view in the channel width direction of the conductor 240b electrically connected to the transistor 200 and functioning as aplug. As illustrated in FIG. 3(B), the conductor 240 b is provided incontact with the top surface of the conductor 242 b. Since the insulator241 b is provided at the side surface of the conductor 240 b, oxygen andimpurities such as hydrogen and water from the insulator 280 can beprevented from diffusing into the conductor 240 b. Note that a similareffect can also be obtained with the conductor 240 a.

As illustrated in FIGS. 1(A) and 1(B) and FIG. 3(B), the conductor 240 bis preferably provided to overlap with at least part of the conductor247. Accordingly, the area occupied by the conductor 240 b and theconductor 247 in a top view can be reduced, leading to miniaturizationor higher integration of the semiconductor device of this embodiment.

As shown in FIG. 1(C), with the bottom surface of the insulator 224 as areference, the height of the bottom surface of the conductor 260 in aregion where the conductor 260 does not overlap with the oxide 230 a andthe oxide 230 b is preferably positioned in a position lower than theheight of the bottom surface of the oxide 230 b. A difference betweenthe level of the bottom surface of the conductor 260 in a region wherethe oxide 230 b does not overlap with the conductor 260 and the level ofthe bottom surface of the oxide 230 b is set to greater than or equal to0 nm and less than or equal to 100 nm, preferably greater than or equalto 3 nm and less than or equal to 50 nm, and further preferably greaterthan or equal to 5 nm and less than or equal to 20 nm.

As described above, the conductor 260, which functions as the gateelectrode, covers the side surface and the top surface of the oxide 230b of the channel formation region, with the oxide 230 c and theinsulator 250 positioned therebetween; this enables the electrical fieldof the conductor 260 to easily affect the entire oxide 230 b of thechannel formation region. Thus, the on-state current of the transistor200 can be increased and the frequency characteristics of the transistor200 can be improved.

Accordingly, a semiconductor device that is miniaturized or highlyintegrated can be provided. Alternatively, a semiconductor deviceincluding a transistor with high on-state current can be provided.Alternatively, a semiconductor device including a transistor with highfrequency characteristics can be provided. Alternatively, asemiconductor device that has stable electrical characteristics withreduced variations in electrical characteristics and higher reliabilitycan be provided. Alternatively, a semiconductor device including atransistor with low off-state current can be provided.

The detailed structure of the semiconductor device including thetransistor 200 according to one embodiment of the present invention isdescribed below.

The conductor 205 is provided to overlap with the oxide 230 and theconductor 260. Furthermore, the conductor 205 is preferably provided tobe embedded in the insulator 214 and the insulator 216.

Here, the conductor 260 sometimes functions as a first gate (alsoreferred to as top gate) electrode. Alternatively, the conductor 205sometimes functions as a second gate (also referred to as bottom gate)electrode. In that case, V_(th) of the transistor 200 can be controlledby changing a potential applied to the conductor 205 independently of apotential applied to the conductor 260. In particular, V_(th) of thetransistor 200 can be higher than 0 V and the off-state current can bereduced by applying a negative potential to the conductor 205. Thus,drain current when a potential applied to the conductor 260 is 0 V canbe lower in the case where a negative potential is applied to theconductor 205 than in the case where the negative potential is notapplied to the conductor 205.

As illustrated in FIG. 1(A), the size of the conductor 205 is preferablylarger than the size of the region of the oxide 230 that does notoverlap with the conductor 242 a or the conductor 242 b. As illustratedin FIG. 1(C), it is particularly preferable that the conductor 205 alsoextend to a region outside an end portion of the oxide 230 thatintersects with the channel width direction. That is, the conductor 205and the conductor 260 preferably overlap with each other with theinsulators therebetween on an outer side of the side surface of theoxide 230 in the channel width direction. A large conductor 205 cansometimes reduce local charging, (referred to as charge up) in atreatment using plasma of a fabrication step after the formation of theconductor 205. Note that one embodiment of the present invention is notlimited thereto. The conductor 205 is at least overlapped with the oxide230 positioned between the conductor 242 a and the conductor 242 b.

Furthermore, with the above structure, the channel formation region canbe electrically surrounded by the electric field of the conductor 260functioning as the first gate electrode and the electric field of theconductor 205 functioning as the second gate electrode. In thisspecification, a transistor structure in which a channel formationregion is electrically surrounded by electric fields of a first gateelectrode and a second gate electrode is referred to as a surroundedchannel (S-channel) structure.

The conductor 205 a is preferably a conductor that inhibits thetransmission of oxygen and impurities such as water and hydrogen. Forexample, titanium, titanium nitride, tantalum, or tantalum nitride canbe used for the conductor 205 a. Moreover, the conductor 205 b ispreferably formed using a conductive material containing tungsten,copper, or aluminum as its main component. Although the conductor 205 isillustrated as having two layers, the conductor 205 can have amultilayer structure with three or more layers.

The insulator 214 and the insulator 272, and the insulator 281preferably function as a barrier insulating film that inhibitsimpurities such as water or hydrogen from entering the transistor 200from the substrate side or from above. Thus, the insulator 214, theinsulator 272, and the insulator 281 are preferably formed using aninsulating material having a function of inhibiting diffusion ofimpurities (through which the impurities are unlikely to pass) such as ahydrogen atom, a hydrogen molecule, a water molecule, a nitrogen atom, anitrogen molecule, a nitrogen oxide molecule (e.g., N₂O, NO, or NO₂), ora copper atom. Alternatively, it is preferable to use an insulatingmaterial having a function of inhibiting diffusion of oxygen (e.g., atleast one of an oxygen atom, an oxygen molecule, and the like) (orthrough which the above oxygen is less likely to pass).

For example, it is preferable that silicon nitride or the like be usedfor the insulator 214, the insulator 272, and the insulator 281.Accordingly, impurities such as water or hydrogen can be inhibited frombeing diffused into the transistor 200 side from the substrate sidethrough the insulator 214. Alternatively, oxygen contained in theinsulator 224 and the like can be prevented from being diffused to thesubstrate side of the insulator 214. Impurities such as water orhydrogen can be inhibited from diffusing into the transistor 200 sidefrom the insulator 280 and/or the conductor 246 and the like, which areprovided above the insulator 272.

The resistivities of the insulator 214, the insulator 272, and theinsulator 281 are preferably low in some cases. For example, by settingthe resistivities of the insulator 214, the insulator 272, and theinsulator 281 to approximately 1×10¹³ Ωcm, the insulator 214, theinsulator 272, and the insulator 281 can reduce charge up of theconductor 205, the conductor 242 or the conductor 260 in a treatmentusing plasma or the like of a fabrication step of a semiconductor devicein some cases. The resistivities of the insulator 214, the insulator272, and the insulator 281 are preferably higher than or equal to 1×10¹⁰Ωcm and lower than or equal to 1×10¹⁵ Ωcm.

The insulator 214 may have a stacked-layer structure. For example, it ispreferable that a stacked-layer structure of an aluminum oxide film anda silicon nitride film be used as the insulator 214. With the aluminumoxide film, oxygen can be supplied to a lower part of the insulator 214.Furthermore, diffusion of impurities such as hydrogen and water thatenter the transistor 200 side from the substrate side can be suppressedby the silicon nitride film.

The insulator 216, the insulator 280, and the insulator 274 preferablyhave a lower permittivity than the insulator 214. When a material with alow permittivity is used for an interlayer film, the parasiticcapacitance generated between wirings can be reduced. For each of theinsulator 216, the insulator 280, and the insulator 274, silicon oxide,silicon oxynitride, silicon nitride oxide, silicon nitride, siliconoxide to which fluorine is added, silicon oxide to which carbon isadded, silicon oxide to which carbon and nitrogen are added, poroussilicon oxide, or the like is used as appropriate, for example.

The insulator 222 and the insulator 224 each have a function of a gateinsulator.

Here, it is preferable that the insulator 224 in contact with the oxide230 release oxygen by heating. In this specification, oxygen that isreleased by heating is referred to as excess oxygen in some cases. Forexample, for the insulator 224, silicon oxide, silicon oxynitride, orthe like is used as appropriate. When an insulator containing oxygen isprovided in contact with the oxide 230, oxygen vacancies in the oxide230 can be reduced and the reliability of the transistor 200 can beimproved.

As the insulator 224, specifically, an oxide material from which part ofoxygen is released by heating is preferably used. An oxide that releasesoxygen by heating is an oxide film in which the amount of releasedoxygen converted into oxygen molecules is greater than or equal to1.0×10¹⁸ molecules/cm³, preferably greater than or equal to 1.0×10¹¹molecules/cm³, further preferably greater than or equal to 2.0×10¹⁹molecules/cm³ or greater than or equal to 3.0×10²⁰ molecules/cm³ in TDS(Thermal Desorption Spectroscopy) analysis. Note that the temperature ofthe film surface in the TDS analysis is preferably higher than or equalto 100° C. and lower than or equal to 700° C., or higher than or equalto 10⁰° C. and lower than or equal to 400° C.

The insulator 222 preferably functions as a barrier insulating film thatinhibits impurities such as water and hydrogen from entering thetransistor 200 from the substrate side. For example, the insulator 222preferably has lower hydrogen permeability than the insulator 224.Surrounding the insulator 224, the oxide 230, and the like by theinsulator 222 and the insulator 272 can inhibit entry of impurities suchas water or hydrogen into the transistor 200 from the outside.

Furthermore, the insulator 222 preferably has a function of inhibitingdiffusion of oxygen (e.g., at least one of an oxygen atom, an oxygenmolecule, and the like) (or is less likely to transmit the aboveoxygen). For example, the insulator 222 preferably has lower oxygenpermeability than the insulator 224. When the insulator 222 has afunction of inhibiting diffusion of oxygen or impurities, diffusion ofoxygen included in the oxide 230 into an area below the insulator 222can be reduced, which is preferable. Furthermore, the conductor 205 canbe inhibited from reacting with oxygen contained in the insulator 224 orthe oxide 230.

As the insulator 222, an insulator containing an oxide of one or both ofaluminum and hafnium, which is an insulating material, is preferablyused. As the insulator containing an oxide of one or both of aluminumand hafnium, aluminum oxide, hafnium oxide, an oxide containing aluminumand hafnium (hafnium aluminate), or the like is preferably used. In thecase where the insulator 222 is formed using such a material, theinsulator 222 functions as a layer that inhibits release of oxygen fromthe oxide 230 and entry of impurities such as hydrogen from theperiphery of the transistor 200 into the oxide 230.

Alternatively, aluminum oxide, bismuth oxide, germanium oxide, niobiumoxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, orzirconium oxide may be added to these insulators, for example.Alternatively, these insulators may be subjected to nitriding treatment.Silicon oxide, silicon oxynitride, or silicon nitride may be stackedover the insulator.

Alternatively, for example, a single layer or stacked layers of aninsulator containing what is called a high-k material such as aluminumoxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconatetitanate (PZT), strontium titanate (SrTiO₃), or (Ba,Sr)TiO₃ (BST) may beused for the insulator 222. With miniaturization and high integration oftransistors, a problem such as leakage current may arise because of athinner gate insulator. When a high-k material is used for an insulatorfunctioning as the gate insulator, a gate potential during operation ofthe transistor can be reduced while the physical thickness of the gateinsulator is kept.

Note that the insulator 222 and the insulator 224 may each have astacked-layer structure of two or more layers. In that case, withoutlimitation to a stacked-layer structure formed of the same material, astacked-layer structure formed of different materials may be employed.

The conductor 247 may also have a structure in which a first conductivelayer and a second conductive layer positioned on an inner side of thefirst conductive layer like the conductor 205. The first conductivelayer of the conductor 247 is preferably a conductor that inhibits thetransmission of oxygen and impurities such as water and hydrogen. Forexample, titanium, titanium nitride, tantalum, or tantalum nitride canbe used. A conductive material containing tungsten, copper, or aluminumas its main component is preferably used for the second conductive layerof the conductor 247. Although the conductor 247 is illustrated ashaving two layers, the conductor 247 can have a multilayer structurewith three or more layers.

An insulator that inhibits the diffusion of oxygen and impurities suchas hydrogen and water like the insulator 241 may be provided at the sidesurface of the conductor 247 like the conductor 240.

The oxide 230 includes the oxide 230 a, the oxide 230 b over the oxide230 a, and the oxide 230 c over the oxide 230 b. Including the oxide 230a below the oxide 230 b makes it possible to inhibit diffusion ofimpurities into the oxide 230 b from the components formed below theoxide 230 a. Moreover, including the oxide 230 c over the oxide 230 bmakes it possible to inhibit diffusion of impurities into the oxide 230b from the components formed above the oxide 230 c.

Note that the oxide 230 preferably has a stacked-layer structure ofoxides that differ in the atomic ratio of metal atoms. Specifically, theatomic ratio of the element M to the constituent elements in the metaloxide used for the oxide 230 a is preferably greater than the atomicratio of the element M to the constituent elements in the metal oxideused for the oxide 230 b. Moreover, the atomic ratio of the element M toIn in the metal oxide used for the oxide 230 a is preferably greaterthan the atomic ratio of the element M to In in the metal oxide used forthe oxide 230 b. Furthermore, the atomic ratio of In to the element M inthe metal oxide used for the oxide 230 b is preferably greater than theatomic ratio of In to the element M in the metal oxide used for theoxide 230 a. A metal oxide that can be used for the oxide 230 a or theoxide 230 b can be used for the oxide 230 c.

The oxide 230 b preferably has crystallinity. For example, a CAAC-OS(c-axis aligned crystalline oxide semiconductor) described later ispreferably used. An oxide having crystallinity, such as a CAAC-OS, has adense structure with small amounts of impurities and defects (oxygenvacancies or the like) and high crystallinity. This can inhibit oxygenextraction from the oxide 230 b by the source electrode or the drainelectrode. This can reduce oxygen extraction from the oxide 230 b evenwhen heat treatment is performed; thus, the transistor 200 is stablewith respect to high temperatures in a manufacturing process (what iscalled thermal budget).

The energy of the conduction band minimum of each of the oxide 230 a andthe oxide 230 c is preferably higher than the energy of the conductionband minimum of the oxide 230 b. In other words, the electron affinityof each of the oxide 230 a and the oxide 230 c is preferably smallerthan the electron affinity of the oxide 230 b.

Here, the energy level of the conduction band minimum gradually changesat junction portions of the oxide 230 a, the oxide 230 b, and the oxide230 c. In other words, the energy level of the conduction band minimumat the junction portions of the oxide 230 a, the oxide 230 b, and theoxide 230 c continuously changes or is continuously connected. To obtainthis, the density of defect states in a mixed layer formed at aninterface between the oxide 230 a and the oxide 230 b and an interfacebetween the oxide 230 b and the oxide 230 c is preferably made low.

Specifically, as the oxide 230 a, a metal oxide with In:Ga:Zn=1:3:4[atomic ratio] or 1:1:0.5 [atomic ratio] is used. As the oxide 230 b, ametal oxide with In:Ga:Zn=4:2:3 [atomic ratio] or 1:1:1 [atomic ratio]is used. As the oxide 230 c, a metal oxide with In:Ga:Zn=1:3:4 [atomicratio], In:Ga:Zn=4:2:3 [atomic ratio], Ga:Zn=2:1 [atomic ratio], orGa:Zn=2:5 [atomic ratio] is used. Specific examples of the oxide 230 chaving a stacked-layer structure include a stacked-layer structure ofIn:Ga:Zn=4:2:3 [atomic ratio] and In:Ga:Zn=1:3:4 [atomic ratio], astacked-layer structure ofIn:Ga:Zn=4:2:3 [atomic ratio] and Ga:Zn=2:1[atomic ratio], a stacked-layer structure of In:Ga:Zn=4:2:3 [atomicratio] and Ga:Zn=2:5 [atomic ratio], and a stacked-layer structure ofIn:Ga:Zn=4:2:3 [atomic ratio] and gallium oxide.

At this time, the oxide 230 b serves as a main carrier path. When theoxide 230 a and the oxide 230 c have the above structure, the density ofdefect states at the interface between the oxide 230 a and the oxide 230b and the interface between the oxide 230 b and the oxide 230 c can bemade low. Thus, the influence of interface scattering on carrierconduction is small, and the transistor 200 can have high on-statecurrent and high frequency characteristics. Note that in the case wherethe oxide 230 c has a stacked-layer structure, in addition to thereduction of density of defect states at the interface between the oxide230 b and the oxide 230 c, the inhibition of diffusion of theconstituent element of the oxide 230 c to the insulator 250 side isexpected. More specifically, since the oxide 230 c has a stacked-layerstructure in which an oxide that does not contain In is positioned inthe upper layer, the diffusion of In to the insulator 250 side can beinhibited. Since the insulator 250 functions as a gate insulator, thetransistor exhibits poor characteristics when In diffuses. Thus, whenthe oxide 230 c has a stacked-layer structure, a highly reliablesemiconductor device can be provided.

A metal oxide functioning as an oxide semiconductor is preferably usedas the oxide 230. For example, a metal oxide whose energy gap is greaterthan or equal to 2 eV, preferably greater than or equal to 2.5 eV, ispreferably used. With use of a metal oxide having such a wide energygap, the off-state current of the transistor can be reduced. With theuse of such a transistor, a semiconductor device with low powerconsumption can be provided.

Electron affinity or conduction band minimum Ec can be obtained from anenergy gap Eg and an ionization potential Ip, which is a differencebetween a vacuum level and an energy of valence band maximum Ev, asshown in FIG. 12. The ionization potential I_(p) can be measured using,for example, an ultraviolet photoelectron spectroscopy (UPS) apparatus.The energy gap E_(g) can be measured using, for example, a spectroscopicellipsometer.

The oxide 243 is provided over the oxide 230 b, and the conductor 242(the conductor 242 a and the conductor 242 b) functioning as the sourceelectrode and the drain electrode is provided over the oxide 243. Thethickness of the conductor 242 is greater than or equal to 1 nm and lessthan or equal to 50 nm, preferably greater than or equal to 2 nm andless than or equal to 25 nm, for example.

For the conductor 242, it is preferable to use a metal element selectedfrom aluminum, chromium, copper, silver, gold, platinum, tantalum,nickel, titanium, molybdenum, tungsten, hafnium, vanadium, niobium,manganese, magnesium, zirconium, beryllium, indium, ruthenium, iridium,strontium, and lanthanum; an alloy containing any of the above metalelements; an alloy containing a combination of the above metal elements;or the like. For example, it is preferable to use tantalum nitride,titanium nitride, tungsten, a nitride containing titanium and aluminum,a nitride containing tantalum and aluminum, ruthenium oxide, rutheniumnitride, an oxide containing strontium and ruthenium, an oxidecontaining lanthanum and nickel, or the like. Tantalum nitride, titaniumnitride, a nitride containing titanium and aluminum, a nitridecontaining tantalum and aluminum, ruthenium oxide, ruthenium nitride, anoxide containing strontium and ruthenium, and an oxide containinglanthanum and nickel are preferable because they are oxidation-resistantconductive materials or materials that retain their conductivity evenafter absorbing oxygen.

The insulator 250 functions as a gate insulator. The insulator 250 ispreferably placed in contact with the top surface of the oxide 230 c.For the insulator 250, silicon oxide, silicon oxynitride, siliconnitride oxide, silicon nitride, silicon oxide to which fluorine isadded, silicon oxide to which carbon is added, silicon oxide to whichcarbon and nitrogen are added, or porous silicon oxide can be used. Inparticular, silicon oxide and silicon oxynitride, which have thermalstability, are preferable.

The insulator 250 is preferably formed using an insulator from whichoxygen is released by heating as in the insulator 224. When an insulatorfrom which oxygen is released by heating is provided as the insulator250 in contact with the top surface of the oxide 230 c, oxygen can beefficiently supplied to the channel formation region of the oxide 230 b.Furthermore, as in the insulator 224, the concentration of impuritiessuch as water or hydrogen in the insulator 250 is preferably reduced.The thickness of the insulator 250 is preferably greater than or equalto 1 nm and less than or equal to 20 nm.

Furthermore, a metal oxide may be provided between the insulator 250 andthe conductor 260. The metal oxide preferably inhibits diffusion ofoxygen from the insulator 250 to the conductor 260. Provision of themetal oxide that inhibits diffusion of oxygen inhibits diffusion ofoxygen from the insulator 250 to the conductor 260. That is, a reductionin the amount of oxygen supplied to the oxide 230 can be inhibited. Inaddition, oxidation of the conductor 260 due to oxygen from theinsulator 250 can be inhibited.

In addition, the metal oxide has a function of part of the gateinsulator in some cases. Therefore, when silicon oxide, siliconoxynitride, or the like is used for the insulator 250, a metal oxidethat is a high-k material with high relative permittivity is preferablyused for the metal oxide. When the gate insulator has a stacked-layerstructure of the insulator 250 and the metal oxide, the stacked-layerstructure can be thermally stable and have high relative permittivity.Thus, a gate potential that is applied during operation of thetransistor can be reduced while the physical thickness of the gateinsulator is maintained. Furthermore, the equivalent oxide thickness(BOT) of the insulator functioning as the gate insulator can be reduced.

Specifically, a metal oxide containing one kind or a plurality of kindsselected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten,titanium, tantalum, nickel, germanium, magnesium, and the like can beused. It is particularly preferable to use an insulator containing anoxide of one or both of aluminum and hafnium, such as aluminum oxide,hafnium oxide, or an oxide containing aluminum and hafnium (hafniumaluminate).

The metal oxide has a function of part of the gate electrode in somecases. In that case, the conductive material containing oxygen ispreferably provided on the channel formation region side. When theconductive material containing oxygen is provided on the channelformation region side, oxygen released from the conductive material iseasily supplied to the channel formation region.

It is particularly preferable to use, for the conductor functioning asthe gate electrode, a conductive material containing oxygen and a metalelement contained in a metal oxide where the channel is formed.Alternatively, a conductive material containing the above metal elementand nitrogen may be used. Alternatively, indium tin oxide, indium oxidecontaining tungsten oxide, indium zinc oxide containing tungsten oxide,indium oxide containing titanium oxide, indium tin oxide containingtitanium oxide, indium zinc oxide, or indium tin oxide to which siliconis added may be used. Furthermore, indium gallium zinc oxide containingnitrogen may be used. With the use of such a material, hydrogencontained in the metal oxide where the channel is formed can be trappedin some cases. Alternatively, hydrogen entering from an externalinsulator or the like can be trapped in some cases.

Although FIG. 1 shows that the conductor 260 has a two-layer structure,the conductor 260 may have a single-layer structure or a stacked-layerstructure of three or more layers.

For the conductor 260 a, it is preferable to use a conductive materialhaving a function of inhibiting diffusion of impurities such as ahydrogen atom, a hydrogen molecule, a water molecule, a nitrogen atom, anitrogen molecule, a nitrogen oxide molecule (N₂O, NO, NO₂, and thelike), and a copper atom. Alternatively, it is preferable to use aconductive material having a function of inhibiting diffusion of oxygen(e.g., at least one of an oxygen atom, an oxygen molecule, and thelike).

In addition, when the conductor 260 a has a function of inhibitingdiffusion of oxygen, the conductivity of the conductor 260 b can beinhibited from being lowered because of oxidation due to oxygencontained in the insulator 250. As a conductive material having afunction of inhibiting oxygen diffusion, for example, tantalum, tantalumnitride, ruthenium, ruthenium oxide, or the like is preferably used.

A conductive material containing tungsten, copper, or aluminum as itsmain component is preferably used for the conductor 260 b. The conductor260 also functions as a wiring and thus is preferably funned using aconductor having high conductivity. For example, a conductive materialcontaining tungsten, copper, or aluminum as its main component can beused. The conductor 260 b may have a stacked-layer structure, forexample, a stacked-layer structure of any of the above conductivematerials and titanium or titanium nitride.

For example, for the insulator 280, silicon oxide, silicon oxynitride,silicon nitride oxide, silicon oxide to which fluorine is added, siliconoxide to which carbon is added, silicon oxide to which carbon andnitrogen are added, porous silicon oxide, or the like is preferablyincluded. In particular, silicon oxide and silicon oxynitride, whichhave thermal stability, are preferable. Materials such as silicon oxide,silicon oxynitride, and porous silicon oxide, in each of which a regioncontaining oxygen released by heating can be easily formed, areparticularly preferable.

The concentration of impurities such as water or hydrogen in theinsulator 280 is preferably lowered. In addition, the top surface of theinsulator 280 may be planarized.

The insulator 282 preferably functions as a barrier insulating film thatinhibits impurities such as water and hydrogen from entering theinsulator 280 from the above. As the insulator 282, an insulator such asaluminum oxide, silicon nitride, or silicon nitride oxide may be used.

The insulator 274 functioning as an interlayer film is preferablyprovided over the insulator 282. As in the insulator 224 or the like,the concentration of impurities such as water or hydrogen in theinsulator 274 is preferably lowered.

For the conductor 240 a and the conductor 240 b, a conductive materialcontaining tungsten, copper, or aluminum as its main component ispreferably used. In addition, the conductor 240 a and the conductor 240b may each have a stacked-layer structure.

In the case where the conductor 240 has a stacked-layer structure, aconductive material having a function of inhibiting the transmission ofan impurity such as water or hydrogen is preferably used for a conductorin contact with the insulator 281, the insulator 274, the insulator 282,the insulator 280, the insulator 273, and the insulator 272. Forexample, tantalum, tantalum nitride, titanium, titanium nitride,ruthenium, ruthenium oxide, or the like is preferably used. A singlelayer or a stacked layer of the conductive material having a function ofinhibiting the transmission of impurities such as water or hydrogen maybe used. The use of the conductive material can prevent oxygen added tothe insulator 280 from being absorbed by the conductor 240 a and theconductor 240 b. Moreover, the mixing of impurities such as water orhydrogen into the oxide 230 through the conductor 240 a and theconductor 240 b from a layer above the insulator 281 can be inhibited.

As the insulator 241 a and the insulator 241 b, an insulator such asaluminum oxide, silicon nitride, or silicon nitride oxide maybe used.Since the insulator 241 a and the insulator 241 b are provided incontact with the insulator 272 and the insulator 273, the mixing ofimpurities such as water or hydrogen into the oxide 230 through theconductor 240 a and the conductor 240 b from the insulator 280 or thelike can be inhibited. In addition, oxygen contained in the insulator280 can be prevented from being absorbed by the conductor 240 a and theconductor 240 b.

The conductor 246 (the conductor 246 a and the conductor 246 b)functioning as a wiring may be provided in contact with a top surface ofthe conductor 240 a and a top surface of the conductor 240 b. Theconductor 246 is preferably formed using a conductive materialcontaining tungsten, copper, or aluminum as its main component.Furthermore, the conductor may have a stacked-layer structure; forexample, stacked layers of the above conductive material, and titaniumor titanium nitride. Note that the conductor may be formed to beembedded in an opening provided in an insulator.

Note that in the semiconductor device illustrated in FIG. 1, a structureis employed where the conductor 240 b, the insulator 241 b, and theconductor 246 b are provided; however, a structure where these are notprovided can be employed.

<Constituent Material of Semiconductor Device>

Constituent materials that can be used for the semiconductor device aredescribed below.

<Substrate>

As a substrate over which the transistor 200 is formed, an insulatorsubstrate, a semiconductor substrate, or a conductor substrate is used,for example. Examples of the insulator substrate include a glasssubstrate, a quartz substrate, a sapphire substrate, a stabilizedzirconia substrate (an yttria-stabilized zirconia substrate or thelike), and a resin substrate. In addition, examples of the semiconductorsubstrate include a semiconductor substrate including silicon,germanium, or the like as a material, and a compound semiconductorsubstrate including silicon carbide, silicon germanium, galliumarsenide, indium phosphide, zinc oxide, or gallium oxide. Anotherexample is a semiconductor substrate in which an insulator region isincluded in the semiconductor substrate, e.g., an SOI (Silicon OnInsulator) substrate. Examples of the conductor substrate include agraphite substrate, a metal substrate, an alloy substrate, and aconductive resin substrate. Other examples include a substrate includinga metal nitride and a substrate including a metal oxide. Other examplesinclude an insulator substrate provided with a conductor or asemiconductor, a semiconductor substrate provided with a conductor or aninsulator, and a conductor substrate provided with a semiconductor or aninsulator. Alternatively, these substrates provided with elements may beused. Examples of the element provided for the substrate include acapacitor, a resistor, a switching element, a light-emitting element,and a memory element.

<Insulator>

Examples of an insulator include an oxide, a nitride, an oxynitride, anitride oxide, a metal oxide, a metal oxynitride, and a metal nitrideoxide, each of which has an insulating property.

As miniaturization and high integration of the transistor progress, forexample, a problem such as leakage current may arise because of athinner gate insulator. When a high-k material is used for the insulatorfunctioning as a gate insulator, the voltage when the transistoroperates can be reduced while keeping the physical thickness of the gateinsulator. In contrast, when a material with low relative permittivityis used for the insulator functioning as an interlayer film, parasiticcapacitance generated between wirings can be reduced. Thus, a materialis preferably selected depending on the function of an insulator.

In addition, examples of the insulator with high relative permittivityinclude gallium oxide, hafnium oxide, zirconium oxide, an oxidecontaining aluminum and hafnium, an oxynitride containing aluminum andhafnium, an oxide containing silicon and hafnium, an oxynitridecontaining silicon and hafnium, and a nitride containing silicon andhafnium.

In addition, examples of the insulator with low relative permittivityinclude silicon oxide, silicon oxynitride, silicon nitride oxide,silicon oxide to which fluorine is added, silicon oxide to which carbonis added, silicon oxide to which carbon and nitrogen are added, poroussilicon oxide, and a resin.

Furthermore, when a transistor using an oxide semiconductor issurrounded by an insulator having a function of inhibiting thetransmission of oxygen and impurities such as hydrogen, the electricalcharacteristics of the transistor can be stable. For the insulatorhaving a function of inhibiting the transmission of oxygen andimpurities such as hydrogen, a single layer or stacked layers of aninsulator containing, for example, boron, carbon, nitrogen, oxygen,fluorine, magnesium, aluminum, silicon, phosphorus, chlorine, argon,gallium, germanium, yttrium, zirconium, lanthanum, neodymium, hafnium,or tantalum is used. Specifically, as the insulator having a function ofinhibiting transmission of oxygen and impurities such as hydrogen, ametal oxide such as aluminum oxide, magnesium oxide, gallium oxide,germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide,neodymium oxide, hafnium oxide, or tantalum oxide; a metal nitride suchas aluminum nitride, aluminum titanium nitride, titanium nitride,silicon nitride oxide or silicon nitride; or the like can be used.

In addition, the insulator functioning as the gate insulator ispreferably an insulator including a region containing oxygen released byheating. For example, when a structure is employed in which siliconoxide or silicon oxynitride including a region containing oxygenreleased by heating is in contact with the oxide 230, oxygen vacanciesincluded in the oxide 230 can be compensated for.

<Conductor>

For the conductor, it is preferable to use a metal element selected fromaluminum, chromium, copper, silver, gold, platinum, tantalum, nickel,titanium, molybdenum, tungsten, hafnium, vanadium, niobium, manganese,magnesium, zirconium, beryllium, indium, ruthenium, iridium, strontium,and lanthanum; an alloy containing the above metal element; an alloycontaining a combination of the above metal elements; or the like. Forexample, it is preferable to use tantalum nitride, titanium nitride,tungsten, a nitride containing titanium and aluminum, a nitridecontaining tantalum and aluminum, ruthenium oxide, ruthenium nitride, anoxide containing strontium and ruthenium, an oxide containing lanthanumand nickel, or the like. Tantalum nitride, titanium nitride, a nitridecontaining titanium and aluminum, a nitride containing tantalum andaluminum, ruthenium oxide, ruthenium nitride, an oxide containingstrontium and ruthenium, and an oxide containing lanthanum and nickelare preferable because they are oxidation-resistant conductive materialsor materials that retain their conductivity even after absorbing oxygen.A semiconductor having high electrical conductivity, typified bypolycrystalline silicon containing an impurity element such asphosphorus, or silicide such as nickel silicide may be used.

A stack including a plurality of conductive layers formed of the abovematerials may be used. For example, a stacked-layer structure combininga material containing the above metal element and a conductive materialcontaining oxygen may be employed. A stacked-layer structure combining amaterial containing the above metal element and a conductive materialcontaining nitrogen may be employed. A stacked-layer structure combininga material containing the above metal element, a conductive materialcontaining oxygen, and a conductive material containing nitrogen may beemployed.

Note that when an oxide is used for the channel formation region of thetransistor, a stacked-layer structure in which a material containing theabove metal element and a conductive material containing oxygen arecombined is preferably used for the conductor functioning as the gateelectrode. In that case, the conductive material containing oxygen ispreferably provided on the channel formation region side. When theconductive material containing oxygen is provided on the channelformation region side, oxygen released from the conductive material iseasily supplied to the channel formation region.

It is particularly preferable to use, for the conductor functioning asthe gate electrode, a conductive material containing oxygen and a metalelement contained in a metal oxide where the channel is formed.Alternatively, a conductive material containing the above metal elementand nitrogen may be used. For example, a conductive material containingnitrogen, such as titanium nitride or tantalum nitride, maybe used.Alternatively, indium tin oxide, indium oxide containing tungsten oxide,indium zinc oxide containing tungsten oxide, indium oxide containingtitanium oxide, indium tin oxide containing titanium oxide, indium zincoxide, or indium tin oxide to which silicon is added may be used.Furthermore, indium gallium zinc oxide containing nitrogen may be used.With use of such a material, hydrogen contained in the metal oxide wherethe channel is formed can be trapped in some cases. Alternatively,hydrogen entering from an external insulator or the like can be trappedin some cases.

<Metal Oxide>

As the oxide 230, a metal oxide functioning as an oxide semiconductor ispreferably used. A metal oxide that can be applied to the oxide 230 ofthe present invention is described below.

The metal oxide preferably contains at least indium or zinc. Inparticular, indium and zinc are preferably contained. Furthermore,aluminum, gallium, yttrium, tin, or the like is preferably contained inaddition to them. Furthermore, one or more kinds selected from boron,titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum,cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the likemay be contained.

Here, the case where the metal oxide is an In-M-Zn oxide containingindium, an element M, and zinc is considered. Note that the element M isaluminum, gallium, yttrium, tin, or the like. Examples of other elementsthat can be used as the element M include boron, titanium, iron, nickel,germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium,tantalum, tungsten, and magnesium. Note that it is sometimes acceptableto use a plurality of the above-described elements in combination as theelement M.

Note that in this specification and the like, a metal oxide containingnitrogen is also collectively referred to as a metal oxide in somecases. A metal oxide containing nitrogen may be referred to as a metaloxynitride.

[Structure of Metal Oxide]

Oxide semiconductors (metal oxides) can be classified into a singlecrystal oxide semiconductor and a non-single-crystal oxidesemiconductor. Examples of the non-single-crystal oxide semiconductorsinclude a CAAC-OS, a polycrystalline oxide semiconductor, an ne-OS, anamorphous-like oxide semiconductor (a-like OS), and an amorphous oxidesemiconductor.

The CAAC-OS has c-axis alignment, a plurality of nanocrystals areconnected in the a-b plane direction, and its crystal structure hasdistortion. Note that the distortion refers to a portion where thedirection of a lattice arrangement changes between a region with aregular lattice arrangement and another region with a regular latticearrangement in a region where the plurality of nanocrystals areconnected.

The nanocrystal is basically a hexagon but is not always a regularhexagon and is a non-regular hexagon in some cases. Furthermore, apentagonal or heptagonal lattice arrangement, for example, is includedin the distortion in some cases. Note that a clear crystal grainboundary (also referred to as grain boundary) is difficult to observeeven in the vicinity of distortion in the CAAC-OS. That is, formation ofa crystal grain boundary is inhibited by the distortion of a latticearrangement. This is because the CAAC-OS can tolerate distortion owingto a low density of arrangement of oxygen atoms in the a-b planedirection, an interatomic bond length changed by substitution of a metalelement, and the like.

Furthermore, the CAAC-OS tends to have a layered crystal structure (alsoreferred to as a layered structure) in which a layer containing indiumand oxygen (hereinafter referred to as an In layer) and a layercontaining the element M, zinc, and oxygen (hereinafter referred to asan (M,Zn) layer) are stacked. Note that indium and the element M can bereplaced with each other, and when the element Min the (M,Zn) layer isreplaced with indium, the layer can also be referred to as an (In,M,Zn)layer. Furthermore, when indium in the In layer is replaced with theelement M, the layer can be referred to as an (In,M) layer.

The CAAC-OS is a metal oxide with high crystallinity. By contrast, inthe CAAC-OS, a reduction in electron mobility due to the crystal grainboundary is less likely to occur because it is difficult to observe aclear crystal grain boundary. Furthermore, entry of impurities,formation of defects, or the like might decrease the crystallinity of ametal oxide, which means that the CAAC-OS is a metal oxide having smallamounts of impurities and defects (e.g., oxygen vacancies (VO)). Thus, ametal oxide including a CAAC-OS is physically stable. Therefore, themetal oxide including a CAAC-OS is resistant to heat and has highreliability.

In the nc-OS, a microscopic region (for example, a region with a sizegreater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic arrangement. Furthermore,there is no regularity of crystal orientation between differentnanocrystals in the nc-OS. Thus, the orientation in the whole film isnot observed. Accordingly, the nc-OS cannot be distinguished from ana-like OS or an amorphous oxide semiconductor depending on the analysismethod.

Note that indium-gallium-zinc oxide (hereinafter referred to as IGZO)that is a kind of metal oxide containing indium, gallium, and zinc has astable structure in some cases by being formed of the above-describednanocrystals. In particular, crystals of IGZO tend not to grow in theair and thus, a stable structure is obtained when IGZO is formed ofsmaller crystals (e.g., the above-described nanocrystals) rather thanlarger crystals (here, crystals with a size of several millimeters orseveral centimeters).

An a-like OS is a metal oxide having a structure between those of thenc-OS and an amorphous oxide semiconductor. The a-like OS includes avoid or a low-density region. That is, the a-like OS has lowcrystallinity compared with the nc-OS and the CAAC-OS.

An oxide semiconductor (metal oxide) can have various structures whichshow different properties. Two or more of the amorphous oxidesemiconductor, the polycrystalline oxide semiconductor, the a-like OS,the nc-OS, and the CAAC-OS may be included in an oxide semiconductor ofone embodiment of the present invention.

Note that a structure of an oxide semiconductor (metal oxide) in thesemiconductor device of one embodiment of the present invention is notparticularly limited; however, the oxide semiconductor (metal oxide)preferably has crystallinity. For example, the oxide 230 can have aCAAC-OS structure and the oxide 243 can have a hexagonal crystalstructure. The semiconductor device can have high reliability when theoxide 230 and the oxide 243 have the above crystal structure.

[Impurities]

Here, the influence of each impurity in the metal oxide will bedescribed.

When the metal oxide contains an alkali metal or an alkaline earthmetal, defect states are formed and carriers are generated in somecases. Thus, a transistor using a metal oxide that contains an alkalimetal or an alkaline earth metal for its channel formation region islikely to have normally-on characteristics. Therefore, it is preferableto reduce the concentration of an alkali metal or an alkaline earthmetal in the metal oxide. Specifically, the concentration of an alkalimetal or an alkaline earth metal in the metal oxide obtained by SIMS(the concentration of an alkali metal or an alkaline earth metalobtained by secondary ion mass spectrometry) is set lower than or equalto 1×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁶ atoms/cm³.

Hydrogen contained in a metal oxide reacts with oxygen bonded to a metalatom to be water, and thus forms an oxygen vacancy in some cases. Entryof hydrogen into the oxygen vacancy generates an electron serving as acarrier in some cases. Furthermore, in some cases, bonding of part ofhydrogen to oxygen bonded to a metal atom causes generation of anelectron serving as a carrier. Thus, a transistor using a metal oxidecontaining hydrogen is likely to have normally-on characteristics.

Accordingly, hydrogen in the metal oxide is preferably reduced as muchas possible.

Specifically, the hydrogen concentration of the metal oxide obtained bySIMS is set lower than 1×10²⁰ atoms/cm³, preferably lower than 1×10¹⁹atoms/cm³, further preferably lower than 5×10¹⁸ atoms/cm³, still furtherpreferably lower than 1×10¹⁸ atoms/cm³. When a metal oxide in which theimpurities are sufficiently reduced is used in a channel formationregion of a transistor, stable electrical characteristics can be given.

Note that as a metal oxide used for a semiconductor of a transistor, athin film having high crystallinity is preferably used. With use of thethin film, the stability or reliability of the transistor can beimproved. Examples of the thin film include a thin film of asingle-crystal metal oxide and a thin film of a polycrystalline metaloxide. However, to form the thin film of a single-crystal metal oxide orthe thin film of a polycrystalline metal oxide over a substrate, ahigh-temperature process or a laser heating process is needed. Thus,manufacturing cost is increased, and throughput is decreased.

Non-Patent Document 1 and Non-Patent Document 2 have reported that anIn—Ga—Zn oxide having a CAAC structure (referred to as CAAC-IGZO) wasfound in 2009. Here, it has been reported that CAAC-IGZO has c-axisalignment, a crystal grain boundary is not clearly observed inCAAC-IGZO, and CAAC-IGZO can be formed over a substrate at lowtemperatures.

It has also been reported that a transistor using CAAC-IGZO hasexcellent electrical characteristics and high reliability.

In addition, an In—Ga—Zn oxide having an nc structure (referred to asnc-IGZO) was found in 2013 (see Non-Patent Document 3). Here, it hasbeen reported that nc-IGZO has periodic atomic arrangement in amicroscopic region (for example, a region with a size greater than orequal to 1 nm and less than or equal to 3 nm) and there is no regularityof crystal orientation between different regions.

Non-Patent Document 4 and Non-Patent Document 5 have shown changes inaverage crystal size due to electron beam irradiation to thin films ofCAAC-IGZO, nc-IGZO, and IGZO having low crystallinity. In the thin filmof IGZO having low crystallinity, crystalline IGZO with a size ofapproximately 1 nm was observed even before electron beam irradiation.Thus, here, it has been reported that the existence of a completelyamorphous structure could not be observed in IGZO. In addition, it hasbeen shown that the thin film of CAAC-IGZO and the thin film of nc-IGZOeach have higher stability to electron beam irradiation than the thinfilm of IGZO having low crystallinity. Thus, the thin film of CAAC-IGZOor the thin film of nc-IGZO is preferably used for the semiconductor ofthe transistor.

Non-Patent Document 6 shows that a transistor using a metal oxide has anextremely low leakage current in an off state; specifically, theoff-state current per micrometer in the channel width of the transistoris of the order of yA/μm (10⁻²⁴ A/μm). For example, a CPU with low powerconsumption utilizing a characteristic of a low leakage current of thetransistor using a metal oxide is disclosed (see Non-Patent Document 7).

Furthermore, application of a transistor using a metal oxide to adisplay device that utilizes the characteristic of a low leakage currentof the transistor has been reported (see Non-Patent Document 8). In thedisplay device, a displayed image is changed several tens of times persecond. The number of times an image is changed per second is referredto as a refresh rate. The refresh rate is also referred to as drivefrequency. Such high-speed screen change that is hard for human eyes torecognize is considered as a cause of eyestrain. Thus, it is proposedthat the refresh rate of the display device is lowered to reduce thenumber of times of image rewriting. Moreover, driving with a loweredrefresh rate can reduce the power consumption of the display device.Such a driving method is referred to as idling stop (IDS) driving.

The discovery of the CAAC structure and the nc structure has contributedto an improvement in electrical characteristics and reliability of atransistor using a metal oxide having the CAAC structure or the ncstructure, a reduction in manufacturing cost, and an improvement inthroughput. Furthermore, applications of the transistor to a displaydevice and an LSI utilizing the property of low leakage current of thetransistor have been studied.

<Fabrication Method of Semiconductor Device>

Next, a method for fabricating a semiconductor device including thetransistor 200 according to the present invention, which is illustratedin FIG. 1, will be described with reference to FIG. 4 to FIG. 11. InFIG. 4 to FIG. 11, (A) of each drawing is a top view. Moreover, (B) ofeach drawing is a cross-sectional view corresponding to a portionindicated by the dashed-dotted line A1-A2 in (A), and is also across-sectional view in the channel length direction of the transistor200. Moreover, (C) in each drawing is a cross-sectional viewcorresponding to a portion indicated by a dashed-dotted line A3-A4 in(A), and is also a cross-sectional view of the transistor 200 in thechannel width direction. Note that for clarity of the drawing, somecomponents are not illustrated in the top view of (A) in each drawing.

First, a substrate (not illustrated) is prepared, and the insulator 214is deposited over the substrate. The insulator 214 can be deposited by asputtering method, a chemical vapor deposition (CVD) method, a molecularbeam epitaxy (MBE) method, a pulsed laser deposition (PLD) method, anALD (Atomic Layer Deposition) method, or the like.

Note that the CVD method can be classified into a plasma enhanced CVD(PECVD) method using plasma, a thermal CVD (TCVD) method using heat, aphoto CVD method using light, and the like. Moreover, the CVD method canbe classified into a metal CVD (MCVD) method and a metal organic CVD(MOCVD) method depending on a source gas to be used.

By a plasma CVD method, a high-quality film can be obtained at arelatively low temperature. Furthermore, a thermal CVD method is adeposition method that does not use plasma and thus enables less plasmadamage to an object to be processed. For example, a wiring, anelectrode, an element (a transistor, a capacitor, or the like), or thelike included in a semiconductor device might be charged up by receivingelectric charge from plasma. In that case, accumulated electric chargemight break the wiring, the electrode, the element, or the like includedin the semiconductor device. In contrast, such plasma damage does notoccur in the case of a thermal CVD method that does not use plasma, andthus the yield of the semiconductor device can be increased. Inaddition, the thermal CVD method does not cause plasma damage duringdeposition, so that a film with few defects can be obtained.

In addition, in an ALD method, one atomic layer can be deposited at atime using self-regulating characteristics of atoms. Thus, the ALDmethod has advantages such as deposition of an extremely thin film,deposition on a component with a high aspect ratio, deposition of a filmwith a small number of defects such as pinholes, deposition with goodcoverage, and low-temperature deposition. Furthermore, the ALD methodincludes a plasma enhanced ALD (PEALD) method that is a depositionmethod using plasma. The use of plasma is sometimes preferable becausedeposition at lower temperature is possible. Note that a precursor usedin the ALD method sometimes contains impurities such as carbon. Thus, insome cases, a film provided by the ALD method contains impurities suchas carbon in a larger amount than a film provided by another depositionmethod. Note that impurities can be quantified by X-ray photoelectronspectroscopy (XPS).

Unlike a film formation method in which particles ejected from a targetor the like are deposited, a CVD method and an ALD method are filmdeposition methods in which a film is deposited by reaction at a surfaceof an object. Thus, a CVD method and an ALD method are film depositionmethods that enable favorable step coverage almost regardless of theshape of an object. In particular, an ALD method has excellent stepcoverage and excellent thickness uniformity and thus is suitable forcovering a surface of an opening with a high aspect ratio, for example.On the other hand, an ALD method has a relatively low deposition rate,and thus is preferably used in combination with another film depositionmethod with a high deposition rate, such as a CVD method, in some cases.

When a CVD method or an ALD method is used, the composition of a film tobe deposited can be controlled with a flow rate ratio of source gases.For example, by a CVD method or an ALD method, a film with a certaincomposition can be deposited depending on the flow rate ratio of thesource gases. Moreover, with a CVD method or an ALD method, by changingthe flow rate ratio of the source gases while depositing the film, afilm whose composition is continuously changed can be formed. In thecase of depositing a film while changing the flow rate ratio of sourcegases, as compared with the case of depositing a film with use of aplurality of deposition chambers, time taken for the deposition can beshortened because time taken for transfer and pressure adjustment is notrequired. Thus, the productivity of the semiconductor device can beincreased in some cases.

In this embodiment, for the insulator 214, silicon nitride is depositedby a CVD method. As described here, an insulator through which coppersuch as silicon nitride is less likely to pass, is used for theinsulator 214; accordingly, even when a metal that is likely to diffusecopper or the like is used for a conductor of a lower layer (notillustrated) of the insulator 214, diffusion of the metal into the upperlayer of the insulator 214 can be inhibited.

Next, the insulator 216 is deposited over the insulator 214. Theinsulator 216 can be deposited by a sputtering method, a CVD method, anMBE method, a PLD method, an ALD method, or the like.

Then, an opening reaching the insulator 214 is formed in the insulator216. Note that examples of the opening include a groove and a slit. Aregion where the opening is formed may be referred to as an openingportion. Wet etching can be used for the formation of the openings;however, dry etching is preferably used for microfabrication. As theinsulator 214, it is preferable to select an insulator that functions asan etching stopper film used in forming the groove by etching theinsulator 216. For example, in the case where a silicon oxide film isused as the insulator 216 in which the groove is to be formed, a siliconnitride film, an aluminum oxide film, or a hafnium oxide film ispreferably used as the insulator 214.

After the formation of the opening, a conductive film to be theconductor 205 is deposited. The conductive film preferably includes aconductor that has a function of inhibiting the transmission of oxygen.For example, tantalum nitride, tungsten nitride, or titanium nitride canbe used. Alternatively, a stacked-layer film with tantalum, tungsten,titanium, molybdenum, aluminum, copper, or a molybdenum-tungsten alloycan be used. The conductive film to be the conductor 205 can bedeposited by a sputtering method, a CVD method, an MBE method, a PLDmethod, an ALD method, or the like.

In this embodiment, the conductive film to be the conductor 205 has amultilayer structure.

First, tantalum nitride is deposited by a sputtering method, andtitanium nitride is stacked over the tantalum nitride. Even when a metalthat is likely to diffuse, such as copper, is used for an upper layer ofthe conductive film to be the conductor 205 described below, the use ofsuch metal nitrides for a lower layer of the conductive film to be theconductor 205 can prevent outward diffusion of the metal from theconductor 205.

Next, a conductive film that is the upper layer of the conductive filmto be the conductor 205 is deposited. The conductive film can bedeposited by a plating method, a sputtering method, a CVD method, an MBEmethod, a PLD method, an ALD method, or the like. In this embodiment,for the conductive film of the upper layer of the conductive film to bethe conductor 205, a low-resistance conductive material such as copperis deposited.

Next, CMP treatment is performed to remove parts of the upper layer ofthe conductive film to be the conductor 205 and the lower layer of theconductive film to be the conductor 205, so that the insulator 216 isexposed. As a result, the conductive film to be the conductor 205remains only in the opening portion. Thus, the conductor 205 whose topsurface is flat can be formed. Note that the insulator 216 is partlyremoved by the CMP treatment in some cases (see FIG. 4).

Here, a method for forming the conductor 205 which is different from theabove will be described below.

Next, the conductive film to be the conductor 205 is deposited over theinsulator 214. The conductive film to be the conductor 205 can bedeposited by a sputtering method, a CVD method, an MBE method, a PLDmethod, an ALD method, or the like. In addition, the conductive film tobe the conductor 205 can be a multilayer film. In this embodiment,tungsten is deposited for the conductive film to be the conductor 205.

Next, the conductive film to be the conductor 205 is processed by alithography method, so that the conductor 205 is formed.

Note that in the lithography method, first, a resist is exposed to lightthrough a mask. Next, a region exposed to light is removed or left usinga developer, so that a resist mask is formed. Then, etching treatmentthrough the resist mask is performed, so that a conductor, asemiconductor, an insulator, or the like can be processed into a desiredshape. The resist mask is formed by, for example, exposure of the resistto light such as KrF excimer laser light, ArF excimer laser light, EUV(Extreme Ultraviolet) light, or the like. Alternatively, a liquidimmersion technique may be employed in which a gap between a substrateand a projection lens is filled with liquid (e.g., water) in lightexposure. Alternatively, an electron beam or an ion beam may be usedinstead of the light Note that a mask is unnecessary in the case ofusing an electron beam or an ion beam. Note that for removal of theresist mask, dry etching treatment such as ashing can be performed, wetetching treatment can be performed, wet etching treatment can beperformed after dry etching treatment, or dry etching treatment can beperformed after wet etching treatment.

In addition, a hard mask formed of an insulator or a conductor may beused instead of the resist mask. In the case where a hard mask is used,a hard mask with a desired shape can be formed by forming an insulatingfilm or a conductive film that is the hard mask material over theconductive film to be the conductor 205, forming a resist maskthereover, and then etching the hard mask material. The etching of theconductive film to be the conductor 205 may be performed after removalof the resist mask or with the resist mask remaining. In the lattercase, the resist mask sometimes disappears during the etching. The hardmask may be removed by etching after the etching of the conductive filmto be the conductor 205. Meanwhile, the hard mask is not necessarilyremoved when the hard mask material does not affect a post-process orcan be utilized in the post-process.

As a dry etching apparatus, a capacitively coupled plasma (CCP) etchingapparatus including parallel plate electrodes can be used. Thecapacitively coupled plasma etching apparatus including the parallelplate electrodes may have a structure in which a high-frequency power isapplied to one of the parallel plate electrodes. Alternatively, astructure may be employed in which different high-frequency powers areapplied to one of the parallel plate electrodes. Alternatively, astructure may be employed in which high-frequency powers with the samefrequency are applied to the parallel plate electrodes. Alternatively, astructure may be employed in which high-frequency powers with differentfrequencies are applied to the parallel plate electrodes. Alternatively,a dry etching apparatus including a high-density plasma source can beused. As the dry etching apparatus including a high-density plasmasource, an inductively coupled plasma (ICP) etching apparatus or thelike can be used, for example.

Next, an insulating film to be the insulator 216 is deposited over theinsulator 214 and the conductor 205. The insulator to be the insulator216 can be deposited by a sputtering method, a CVD method, an MBEmethod, a PLD method, an ALD method, or the like. In this embodiment,for the insulating film to be the insulator 216, silicon oxide isdeposited by a CVD method.

Here, the thickness of the insulating film to be the insulator 216 ispreferably greater than or equal to the thickness of the conductor 205.For example, when the thickness of the conductor 205 is 1, the thicknessof the insulating film to be the insulator 216 is greater than or equalto 1 and less than or equal to 3. In this embodiment, the thickness ofthe thickness of the conductor 205 is 150 nm and the thickness of theinsulating film to be the insulator 216 is 350 nm.

Next, CMP (chemical Mechanical Polishing) treatment is performed on theinsulating film to be the insulator 216, so that part of the insulatingfilm to be the insulator 216 is removed and a surface of the conductor205 is exposed. Thus, the conductor 205 and the insulator 216 whose topsurfaces are flat can be formed. The above is the different method forforming the conductor 205. FIG. 2 illustrates an example of asemiconductor device including the transistor 200 in which the conductor205 and the insulator 216 are formed in the above manner.

Next, the insulator 222 is deposited over the insulator 216 and theconductor 205. An insulator containing an oxide of one or both ofaluminum and hafnium is preferably deposited as the insulator 222. Notethat as the insulator containing an oxide of one or both of aluminum andhafnium, aluminum oxide, hafnium oxide, an oxide containing aluminum andhafnium (hafnium aluminate), or the like is preferably used. Theinsulator containing an oxide of one or both of aluminum and hafnium hasa barrier property against oxygen, hydrogen, and water. When theinsulator 222 has a barrier property against hydrogen and water,hydrogen and water contained in components provided around thetransistor 200 are inhibited from being diffused into the transistor 200through the insulator 222, and generation of oxygen vacancies in theoxide 230 can be inhibited.

The insulator 222 can be deposited by a sputtering method, a CVD method,an MBE method, a PLD method, an ALD method, or the like.

Next, the insulator 224 is deposited over the insulator 222. Theinsulator 224 can be deposited by a sputtering method, a CVD method, anMBE method, a PLD method, an AUD method, or the like.

Then, an opening is formed in the insulator 224, the insulator 222, theinsulator 216, and the insulator 214. Wet etching can be used for theformation of the opening; however, dry etching is preferably used formicrofabrication.

After the formation of the opening, a conductive film to be theconductor 247 is deposited. The conductive film preferably includes aconductor that has a function of inhibiting the transmission of oxygen.For example, tantalum nitride, tungsten nitride, or titanium nitride canbe used. Alternatively, a stacked-layer film with tantalum, tungsten,titanium, molybdenum, aluminum, copper, or a molybdenum-tungsten alloycan be used. The conductive film to be the conductor 247 can bedeposited by a sputtering method, a CVD method, an MBE method, a PLDmethod, an ALD method, or the like.

Next, CMP treatment is performed to remove part of the conductive filmto be the conductor 247, so that the insulator 224 is exposed. As aresult, the conductive film to be the conductor 247 remains only in theopening portion. Thus, the conductor 247 whose top surface is flat canbe formed. Note that the insulator 224 is partly removed by the CMPtreatment in some cases (see FIG. 4).

Next, heat treatment is preferably performed. The heat treatment may beperformed at a temperature higher than or equal to 250° C. and lowerthan or equal to 650° C., preferably higher than or equal to 300° C. andlower than or equal to 500° C., further preferably higher than or equalto 320° C. and lower than or equal to 450° C. Note that the heattreatment is performed in a nitrogen or inert gas atmosphere, or anatmosphere containing an oxidizing gas at 10 ppm or more, 1% or higher,or 10% of higher. Alternatively, the heat treatment may be performedunder reduced pressure. Alternatively, the heat treatment may beperformed by performing heat treatment in a nitrogen or inert gasatmosphere and then performing heat treatment in an atmospherecontaining an oxidizing gas at 10 ppm or higher, 1% or higher, or 10% orhigher to compensate for released oxygen.

In this embodiment, treatment is performed at 400° C. in a nitrogenatmosphere for 1 hour, and treatment is successively performed at 400°C. in an oxygen atmosphere for 1 hour. By the heat treatment, impuritiessuch as water and hydrogen contained in the insulator 224 can beremoved.

The above heat treatment may be performed after the insulator 222 isdeposited. For the heat treatment, the conditions for theabove-described heat treatment can be used.

Here, in order to form an excess-oxygen region in the insulator 224,plasma treatment containing oxygen may be performed under reducedpressure. For the plasma treatment containing oxygen, an apparatusincluding a power source for generating high-density plasma usingmicrowaves is preferably used, for example. Alternatively, a powersource for applying an RF (Radio Frequency) to a substrate side may beincluded. The use of high-density plasma enables high-density oxygenradicals to be produced, and RF application to the substrate side allowsthe oxygen radicals produced by the high-density plasma to beefficiently introduced into the insulator 224. Alternatively, afterplasma treatment containing an inert gas is performed with thisapparatus, plasma treatment containing oxygen may be performed tocompensate for released oxygen. Note that impurities such as water andhydrogen contained in the insulator 224 can be removed by selecting theconditions for the plasma treatment as appropriate. In that case, theheat treatment does not need to be performed.

Here, aluminum oxide may be deposited over the insulator 224 by asputtering method and the aluminum oxide may be subjected to CMP untilthe insulator 224 is reached. The CMP treatment can planarize thesurface of the insulator 224 and smooth the surface of the insulator224. When the CMP treatment is performed on the aluminum oxide placedover the insulator 224, it is easy to detect the endpoint of CMP.Although part of the insulator 224 is polished by CMP and the thicknessof the insulator 224 is reduced in some cases, the thickness can beadjusted when the insulator 224 is deposited. Planarizing and smoothingthe surface of the insulator 224 can improve the coverage with an oxidedeposited later and a decrease in the yield of the semiconductor devicein some cases. The deposition of aluminum oxide over the insulator 224by a sputtering method is preferred because oxygen can be added to theinsulator 224.

Next, an oxide film 230A to be the oxide 230 a and an oxide film 230B tobe the oxide 230 b are deposited in this order over the insulator 224and over the conductor 247 (see FIG. 4). Note that the oxide films arepreferably deposited successively without being exposed to anatmospheric environment. By the deposition without exposure to the air,impurities or moisture from the atmospheric environment can be preventedfrom being attached onto the oxide film 230A and the oxide film 230B, sothat the vicinity of an interface between the oxide film 230A and theoxide film 230B can be kept clean.

The oxide film 230A and the oxide film 230B can be deposited by asputtering method, a CVD method, an MBE method, a PLD method, an ALDmethod, or the like.

In the case where the oxide film 230A and the oxide film 230B aredeposited by a sputtering method, for example, oxygen or a mixed gas ofoxygen and a rare gas is used as a sputtering gas. Increasing theproportion of oxygen contained in the sputtering gas can increase theamount of excess oxygen in the deposited oxide films. In the case wherethe above oxide films are deposited by a sputtering method, the aboveIn-M-Zn oxide target can be used.

In particular, part of oxygen contained in the sputtering gas issupplied to the insulator 224 during the deposition of the oxide film230A in some cases. Therefore, the proportion of oxygen contained in thesputtering gas for the oxide film 230A is higher than or equal to 70%,preferably higher than or equal to 80%, further preferably 100%.

In addition, in the case where the oxide film 230B is formed by asputtering method, when the proportion of oxygen contained in thesputtering gas is higher than or equal to 1% and lower than or equal to30%, preferably higher than or equal to 5% and lower than or equal to20% during the deposition, an oxygen-deficient oxide semiconductor isformed. In a transistor in which an oxygen-deficient oxide semiconductoris used for its channel formation region, comparatively highfield-effect mobility can be obtained.

In this embodiment, the oxide film 230A is deposited by a sputteringmethod using a target with In:Ga:Zn=1:1:0.5 [atomic ratio] (2:2:1[atomic ratio]) or 1:3:4 [atomic ratio]. In addition, the oxide film230B is deposited by a sputtering method using a target withIn:Ga:Zn=4:2:4.1 [atomic ratio] or 1:1:1 [atomic ratio]. Note that eachof the oxide films is formed to have characteristics required for theoxide 230 by selecting the deposition condition and the atomic ratio asappropriate.

Next, heat treatment may be performed. For the heat treatment, theconditions for the above heat treatment can be used. Through the heattreatment, impurities such as water and hydrogen in the oxide film 230Aand the oxide film 230B can be removed, for example. In this embodiment,treatment is performed at 400° C. in a nitrogen atmosphere for 1 hour,and treatment is successively performed at 400° C. in an oxygenatmosphere for 1 hour.

Next, a conductive film 243A is deposited over the oxide film 230B. Theoxide film 243A can be deposited by a sputtering method, a CVD method,an MBE method, a PLD method, an ALD method, or the like (see FIG. 4).

Next, the oxide film 230A, the oxide film 230B, and the oxide film 243Aare processed into island shapes to form the oxide 230 a, the oxide 230b, and an oxide layer 243B (see FIG. 5). Here, at least part of the topsurface of the conductor 247 is exposed from the oxide film 230A, theoxide film 230B, and the oxide film 243A. Alternatively, the oxide film230A, the oxide film 230B, and the oxide film 243A are prevented fromoverlapping with the conductor 247. Note that in this step, although notillustrated, the thickness of a region of the insulator 224 that doesnot overlap with the oxide 230 a is reduced in some cases.

Note that the oxide 230 a, the oxide 230 b, and the oxide layer 243B areformed to at least partly overlap with the conductor 205. It ispreferable that the side surfaces of the oxide 230 a, the oxide 230 b,and the conductive layer 243B be substantially perpendicular to the topsurface of the insulator 222. When the side surfaces of the oxide 230 a,the oxide 230 b, and the oxide layer 243B are substantiallyperpendicular to the top surface of the insulator 222, reduction in areaand higher integration can be achieved when a plurality of thetransistors 200 is provided. Alternatively, a structure may be employedin which an angle formed by the side surfaces of the oxide 230 a, theoxide 230 b, and the oxide layer 243B and the top surface of theinsulator 222 is a small angle. In that case, the angle formed by theside surfaces of the oxide 230 a, the oxide 230 b, and the oxide layer243B and the top surface of the insulator 222 is preferably greater thanor equal to 60° and less than 70°. With such a shape, in a later step,the coverage with the insulator 272 and the like can be improved, sothat defects such as a void can be reduced.

Note that for the processing of the oxide films and the conductive film,a lithography method can be employed. A dry etching method or a wetetching method can be used for the processing. Processing by a dryetching method is suitable for microfabrication.

Then, a conductive film 242A is deposited over the insulator 224, theoxide 230 a, the oxide 230 b, and the oxide layer 243B. The conductivefilm 242A can be deposited by a sputtering method, a CVD method, an MBEmethod, a PLD method, an ALD method, or the like (see FIG. 5).

Next, the conductive film 242A is processed into an island shape,whereby a conductor layer 242B is formed (see FIG. 6). Here, theconductor layer 242B is made to be in contact with at least part of thetop surface of the conductor 247. Alternatively, the conductor layer242B is made to cover the top surface of the conductor 247. Note that inthis step, although not illustrated, the thickness of the region of theinsulator 224 that does not overlap with the conductor layer 242B isreduced in some cases.

It is preferable that a curved surface is included between the sidesurface of the conductor layer 242B and the top surface of the conductorlayer 242B. That is, an end portion of the side surface and an endportion of the top surface are preferably curved (hereinafter, alsoreferred to as a rounded shape). The radius of curvature of the curvedsurface at an end portion of the conductor layer 242B is greater than orequal to 3 nm and less than or equal to 10 nm, preferably greater thanor equal to 5 nm and less than or equal to 6 nm, for example. When theend portions are not angular, coverage with films in later depositionsteps is improved.

Note that for the processing of the conductive films, a lithographymethod can be employed. A dry etching method or a wet etching method canbe used for the processing. Processing by a dry etching method issuitable for microfabrication.

Next, an insulating film 272A is deposited over the insulator 224, theoxide 230 a, the oxide 230 b, the oxide layer 243B, and the conductorlayer 242B (see FIG. 6).

The insulating film 272A can be deposited by a sputtering method, a CVDmethod, an MBE method, a PLD method, an ALD method, or the like. As theinsulating film 272A, an insulating film having a function of inhibitingthe transmission of oxygen is preferably used. For example, siliconnitride, silicon oxide, or aluminum oxide is deposited by a sputteringmethod.

Then, an insulating film 273A is deposited over the insulating film272A. The insulating film 273A can be deposited by a sputtering method,a CVD method, an MBE method, a PLD method, an ALD method, or the like.For example, an aluminum oxide film is preferably deposited by an ALDmethod or a sputtering method. In this embodiment, an aluminum oxidefilm is deposited by an ALD method (see FIG. 6).

Next, an insulating film to be the insulator 280 is deposited over theinsulating film 273A. The insulating film to be the insulator 280 can bedeposited by a sputtering method, a CVD method, an MBE method, a PLDmethod, an ALD method, or the like. Next, the insulating film to be theinsulator 280 is subjected to CMP treatment, so that the insulator 280having a flat top surface is formed (see FIG. 7).

Then, part of the insulator 280, part of the insulating film 273A, partof the insulating film 272A, part of the conductor layer 242B, and partof the oxide layer 243B are processed to form an opening reaching theoxide 230 b. The opening is preferably formed to overlap with theconductor 205. The oxide 243 a, the oxide 243 b, the conductor 242 a,the conductor 242 b, the insulator 272, and the insulator 273 are formedby forming the opening (see FIG. 7).

Part of the insulator 280, part of the insulating film 273A, part of theinsulating film 272A, part of the conductor layer 242B, and part of theoxide layer 243B maybe processed under different conditions. Forexample, part of the insulator 280 may be processed by a dry etchingmethod, part of the insulating film 273A may be processed by a wetetching method, and part of the insulating film 272A, part of theconductor layer 242B, and part of the oxide layer 243B may be processedby a dry etching method.

In some cases, treatment such as dry etching performed in the aboveprocess causes the attachment or diffusion of impurities due to anetching gas or the like to a surface or an inside of the oxide 230 a,the oxide 230 b, or the like. Examples of the impurities includefluorine and chlorine.

In order to remove the impurities and the like, cleaning is performed.Examples of a cleaning method include wet cleaning using a cleaningsolution or the like, plasma treatment using plasma, and cleaning byheat treatment, and these cleanings may be performed in appropriatecombination.

As the wet cleaning, cleaning treatment may be performed using anaqueous solution obtained by diluting an oxalic acid, a phosphoric acid,ammonia water, a hydrofluoric acid, or the like with carbonated water orpure water. Alternatively, ultrasonic cleaning using pure water orcarbonated water may be performed.

Next, heat treatment may be performed. Heat treatment may be performedunder reduced pressure, and an oxide film 230C may be successivelydeposited without exposure to the air. The treatment can remove moistureand hydrogen adsorbed onto the surface of the oxide 230 b and the like,and further can reduce the moisture concentration and the hydrogenconcentration of the oxide 230 a and the oxide 230 b. The heat treatmentis preferably performed In this embodiment, the heat treatment isperformed at 200° C. (see FIG. 8).

Here, it is preferable that the oxide film 230C be provided in contactwith at least part of the side surface of the oxide 230 a, part of theside surface and part of the top surface of the oxide 230 b, part of theside surface of the oxide 243, part of the side surface of the conductor242, the side surface of the insulator 272, the side surface of theinsulator 273, and the side surface of the insulator 280. When theconductor 242 is surrounded by the oxide 243, the insulator 272, and theoxide film 230C, a decrease in the conductivity of the conductor 242 dueto oxidation can be inhibited in a later step.

The oxide film 230C can be deposited by a sputtering method, a CVDmethod, an MBE method, a PLD method, an ALD method, or the like. Theoxide film 230C is deposited by a deposition method similar to that forthe oxide film 230A or the oxide film 230B depending on characteristicsrequired for the oxide film 230C. In this embodiment, the oxide film230C is deposited by a sputtering method using a target withIn:Ga:Zn=4:2:4.1 [atomic ratio].

The oxide film 230C may have a stacked-layer structure. For example, theoxide film 230C may be deposited by a sputtering method using a targetof In:Ga:Zn=4:2:4.1 [atomic ratio] and successively deposited using atarget of In:Ga:Zn=1:3:4 [atomic ratio].

In particular, in the deposition of the oxide film 230C, part of oxygencontained in the sputtering gas is sometimes supplied to the oxide 230 aand the oxide 230 b. Therefore, the proportion of oxygen contained inthe sputtering gas for the oxide film 230C is higher than or equal to70%, preferably higher than or equal to 80%, further preferably 100%.

Next, heat treatment may be performed. Heat treatment may be performedunder reduced pressure, and an insulating film 250A may be successivelydeposited without exposure to the air. The treatment can remove moistureand hydrogen adsorbed onto the surface of the oxide film 230C and thelike, and further can reduce the moisture concentration and the hydrogenconcentration of the oxide 230 a, the oxide 230 b, and the oxide film230C. The heat treatment is preferably performed at a temperature higherthan or equal to 100° C. and lower than or equal to 400° C. (see FIG.9).

The insulating film 250A can be deposited by a sputtering method, a CVDmethod, an MBE method, a PLD method, an ALD method, or the like. For theinsulating film 250A, silicon oxynitride is preferably deposited by aCVD method. Note that the deposition temperature at the time of thedeposition of the insulating film 250A is preferably higher than orequal to 350° C. and lower than 450° C., particularly preferablyapproximately 400° C. When the insulating film 250A is deposited at 400°C., an insulator having few impurities can be deposited.

Next, a conductive film 260Aa and a conductive film 260Ab are deposited.The conductive film 260Aa and the conductive film 260Ab can be depositedby a sputtering method, a CVD method, an MBE method, a PLD method, anALD method, or the like. A CVD method is preferably used, for example.In this embodiment, the conductive film 260Aa is deposited by an ALDmethod, and the conductive film 260Ab is deposited by a CVD method (seeFIG. 10).

Then, the oxide film 230C, the insulating film 250A, the conductive film260Aa, and the conductive film 260Ab are polished by CMP treatment untilthe insulator 280 is exposed, so that the oxide 230 c, the insulator250, and the conductor 260 (the conductor 260 a and the conductor 260 b)are formed (see FIG. 11).

Here, the conductor 242 is surrounded by the oxide 243, the insulator272, and the oxide 230 c; therefore, a decrease in conductivity of theconductor 242 due to oxidation can be inhibited.

Next, heat treatment may be performed. In this embodiment, the treatmentis performed at 400° C. in a nitrogen atmosphere for one hour. The heattreatment can reduce the moisture concentration and the hydrogenconcentration in the insulator 250 and the insulator 280.

Next, an insulating film to be the insulator 282 may be formed over theconductor 260, the oxide 230 c, the insulator 250, and the insulator280. The insulating film to be the insulator 282 can be deposited by asputtering method, a CVD method, an MBE method, a PLD method, an ALDmethod, or the like. An aluminum oxide is preferably deposited as theinsulating film to be the insulator 282 by a sputtering method, forexample. It is preferable to form the insulator 282 in contact with thetop surface of the conductor 260 in this manner because oxygen includedin the insulator 280 can be inhibited from being absorbed into theconductor 260 in a later heat treatment (see FIG. 11).

Next, heat treatment may be performed. In this embodiment, the treatmentis performed at 400° C. in a nitrogen atmosphere for one hour. By theheat treatment, oxygen added by the deposition of the insulator 282 canbe injected into the insulator 280. In addition, the oxygen can beinjected into the oxide 230 a and the oxide 230 b through the oxide 230c.

Next, an insulator to be the insulator 274 may be deposited over theinsulator 282. An insulating film to be the insulator 274 can bedeposited by a sputtering method, a CVD method, an MBE method, a PLDmethod, an ALD method, or the like (see FIG. 11).

Next, an insulator to be the insulator 281 may be deposited over theinsulator 274. An insulating film to be the insulator 281 can bedeposited by a sputtering method, a CVD method, an MBE method, a PLDmethod, an ALD method, or the like. Silicon nitride is preferablydeposited as the insulating film to be the insulator 281 by a sputteringmethod, for example (see FIG. 11).

Next, openings reaching the conductor 242 a and the conductor 242 b areformed in the insulator 272, the insulator 273, the insulator 280, theinsulator 282, the insulator 274, and the insulator 281. The openingsare formed by a lithography method.

Next, an insulating film to be the insulator 241 is deposited and theinsulating film is subjected to anisotropic etching, so that theinsulator 241 is formed. The conductive film can be deposited by asputtering method, a CVD method, an MBE method, a PLD method, an ALDmethod, or the like. As the insulating film to be the insulator 241, aninsulating film having a function of inhibiting the transmission ofoxygen is preferably used. For example, aluminum oxide or siliconnitride is preferably deposited by an ALD method. For the anisotropicetching, a dry etching method or the like may be employed, for example.When the side wall portions of the openings have such a structure,transmission of oxygen from the outside can be inhibited and oxidationof the conductor 240 a and the conductor 240 b to be formed next can beprevented. Furthermore, impurities such as water and hydrogen can beprevented from diffusing from the conductor 240 a and the conductor 240b to the outside.

Next, a conductive film to be the conductor 240 a and the conductor 240b is deposited. The conductive film to be the conductor 240 a and theconductor 240 b desirably has a stacked-layer structure which includes aconductor having a function of inhibiting transmission of impuritiessuch as water and hydrogen. For example, a stacked layer of tantalumnitride, titanium nitride, or the like and tungsten, molybdenum, copper,or the like can be employed. A conductive film to be the conductor 240can be deposited by a sputtering method, a CVD method, an MBE method, aPLD method, an ALD method, or the like.

Next, CMP treatment is performed to remove part of the conductive filmto be the conductor 240 a and the conductor 240 b, so that the insulator281 is exposed. As a result, the conductive film remains only in theopenings, so that the conductor 240 a and the conductor 240 b havingflat top surfaces can be formed (see FIG. 1). Note that the insulator281 is partly removed by the CMP treatment in some cases.

Next, a conductive film to be the conductor 246 is deposited. Theconductive film to be the conductor 246 can be deposited by a sputteringmethod, a CVD method, an MBE method, a PLD method, an ALD method, or thelike.

Next, the conductive film to be the conductor 246 is processed by alithography method to form the conductor 246 a in contact with the topsurface of the conductor 240 a and the conductor 246 b in contact withthe top surface of the conductor 240 b (see FIG. 1).

Through the above process, the semiconductor device including thetransistor 200 illustrated in FIG. 1 can be fabricated. As illustratedin FIG. 4 to FIG. 11, with the use of the method of fabricating thesemiconductor device described in this embodiment, the transistor 200can be fabricated.

According to one embodiment of the present invention, a semiconductordevice that can be miniaturized or highly integrated can be provided.Alternatively, according to one embodiment of the present invention, asemiconductor device with excellent electrical characteristics can beprovided. According to one embodiment of the present invention, asemiconductor device with a high on-state current can be provided.Alternatively, according to one embodiment of the present invention, asemiconductor device with excellent frequency characteristics can beprovided. Alternatively, according to one embodiment of the presentinvention, a highly reliable semiconductor device can be provided.Alternatively, according to one embodiment of the present invention, asemiconductor device with low off-state current can be provided.Alternatively, according to one embodiment of the present invention, asemiconductor device with reduced power consumption can be provided.Alternatively, according to one embodiment of the present invention, asemiconductor device with high productivity can be provided.

<Modification Example of Semiconductor Device>

An example of a semiconductor device including the transistor 200 of oneembodiment of the present invention which is different from thesemiconductor device described in <Structure example of semiconductordevice> above will be described below with reference to FIG. 13 to FIG.23.

Note that in the semiconductor device illustrated in FIG. 13 to FIG. 23,components having the same functions as the components in thesemiconductor device described in <Structure example of semiconductordevice> (see FIG. 1) are denoted by the same reference numerals.

Note that in this section, the materials described in detail in<Structure example of semiconductor device> can be used as theconstituent materials for the transistor 200.

<Modification Example 1 of Semiconductor Device>

FIG. 13(A) and FIG. 13(B) are a top view and a cross-sectional view of asemiconductor device of one embodiment of the present inventionincluding the transistor 200 and a capacitor 100.

In FIG. 13, FIG. 13(A) illustrates a top view. Furthermore, FIG. 13(B)is a cross-sectional view corresponding to a portion indicated by adashed-dotted line A1-A2 in FIG. 13(A), and is also a cross-sectionalview of the transistor 200 in the channel length direction. For clarityof the drawing, some components are not illustrated in the top view ofFIG. 13(A).

The semiconductor device illustrated in FIG. 13 includes the capacitor100 and the transistor 200 over the capacitor 100. The semiconductordevice illustrated in FIG. 13 is different from the semiconductor deviceillustrated in FIG. 1 in that the capacitor 100 is provided under theconductor 247. Note that the transistor 200 illustrated in FIG. 13 isthe same as the transistor 200 illustrated in FIG. 1 except that theconductor 240 b, the insulator 241 b, and the conductor 246 b are notprovided.

The capacitor 100 includes an insulator 114 over an insulator 116, aninsulator 140 over the insulator 114, a conductor 110 positioned in anopening formed in the insulator 114 and the insulator 140, an insulator130 over the conductor 110 and the insulator 140, a conductor 120 overthe insulator 130, and an insulator 150 over the conductor 120 and theinsulator 130. Here, at least parts of the conductor 110, the insulator130, and the conductor 120 are positioned in the opening formed in theinsulator 114 and the insulator 140.

The conductor 110 functions as a lower electrode of the capacitor 100,the conductor 120 functions as an upper electrode of the capacitor 100,and the insulator 130 functions as a dielectric of the capacitor 100. Inthe capacitor 100, the upper electrode and the lower electrode face eachother with the dielectric positioned therebetween on the side surface aswell as the bottom surface of the opening in the insulator 114 and theinsulator 140; thus, the capacitance per unit area can be increased. Andthe deeper the opening is, the larger the capacitance of the capacitor100 can be. Increasing the capacitance per unit area of the capacitor100 in this manner can promote miniaturization or higher integration ofa semiconductor device.

An insulator that can be used as the insulator 280 can be used as theinsulator 114 and the insulator 150. The insulator 116 and the insulator140 preferably function as an etching stopper at the time of forming theopening in the insulator 114 and are formed using an insulator that canbe used as the insulator 214.

The shape of the opening formed in the insulator 114 and the insulator140 when seen from above may be a quadrangular shape, a polygonal shapeother than a quadrangular shape, a polygonal shape with rounded corners,or a circular shape including an elliptical shape. Here, the area wherethe opening and the transistor 200 overlap with each other is preferablylarger in the top view. Such a structure can reduce the area occupied bythe semiconductor device including the capacitor 100 and the transistor200.

The conductor 110 is provided in contact with the opening formed in theinsulator 140, the insulator 114, and the insulator 116. Preferably, thetop surface of the conductor 110 is substantially aligned with the topsurface of the insulator 140. The conductor 110 is preferably formed byan ALD method, a CVD method, or the like and is deposited using aconductor that can be used as the conductor 205, for example.

The insulator 130 is positioned to cover the conductor 110 and theinsulator 140. For the insulator 130, a high-k material such as hafniumoxide, hafnium silicate (HfSi_(x)O_(y) (x>0, y>0)), hafnium silicate towhich nitrogen is added (HfSi_(x)O_(y)N_(z) (x>0, y>0, z>0)), hafniumaluminate to which nitrogen is added (HfAl_(x)O_(y)N_(z) (x>0, y>0,z>0)), or yttrium oxide. The use of such a high-k material can securesufficient capacitance of the capacitor 100 even if the insulator 130has a large thickness. When the insulator 130 has a large thickness,leakage current generated between the conductor 110 and the conductor120 can be inhibited. The insulator 130 is preferably deposited by anALD method or a CVD method, for example.

Note that the insulator 130 can be provided by stacking a material withhigh dielectric strength such as silicon oxynitride (a material with lowrelative permittivity) over an insulator of the above-mentioned high-kmaterial. Examples of the material with high dielectric strength includesilicon oxide, silicon oxynitride, silicon nitride oxide, siliconnitride, silicon oxide to which fluorine is added, silicon oxide towhich carbon is added, silicon oxide to which carbon and nitrogen areadded, porous silicon oxide, and a resin. In the capacitor 100, bystacking the insulator 130 in such a manner, a sufficient capacitancecan be secured owing to the insulator of the high-k material, and thedielectric strength can be increased owing to the insulator with highdielectric strength, so that the electrostatic breakdown of thecapacitor 100 can be prevented. Note that in the case where sufficientcapacitance of the capacitor 100 can be secured, the insulator 130 canbe formed only with a material with high dielectric strength.

The conductor 120 is positioned to fill the opening formed in theinsulator 140 and the insulator 114. The conductor 247 is in contactwith the top surface of the conductor 120 through an opening in theinsulator 150. The conductor 120 is preferably deposited by an ALDmethod, a CVD method, or the like and is formed using a conductor thatcan be used as the conductor 205, for example.

In the fabrication process of the capacitor 100, high-temperature heattreatment of higher than 700° C. is needed in some cases. When such ahigh-temperature heat treatment is performed after the formation of thetransistor 200, the oxide 230 might be affected by the diffusion ofoxygen or impurities such as hydrogen or water, which might degrade theelectrical characteristics of the transistor 200.

However, when the transistor 200 is formed over the capacitor 100 asdescribed in this modification example, the thermal budget in thefabrication process of the capacitor 100 does not affect the transistor200. Thus, degradation in electrical characteristics of the transistor200 can be prevented and a semiconductor device having stable electricalcharacteristics can be provided.

Note that although, in this modification example, the conductor 242 band the conductor 120 are electrically connected to each other throughthe conductor 247, this modification example is not limited thereto. Forexample, the capacitor 100 maybe provided so that the top surface of theconductor 120 is exposed from the insulator 224, and the top surface ofthe conductor 120 may be in contact with the conductor 242 b.

<Modification Example 2 of Semiconductor Device>

FIG. 14(A) and FIG. 14(B) are a top view and a cross-sectional view of asemiconductor device of one embodiment of the present inventionincluding the transistor 200 and a capacitor 100 a.

In FIG. 14, FIG. 14(A) illustrates a top view of a layer including theinsulator 140 (an insulator 140 a and an insulator 140 b). Furthermore,FIG. 14(B) is a cross-sectional view corresponding to a portionindicated by a dashed-dotted line A1-A2 in FIG. 14(A), and is also across-sectional view of the transistor 200 in the channel lengthdirection.

The semiconductor device illustrated in FIG. 14 is different from thesemiconductor device illustrated in FIG. 13 in that the shape of thecapacitor 100 a is different from that of the capacitor 100. Thecapacitor 100 a includes an insulator 114 a, an insulator 114 b, theinsulator 140 a, the insulator 140 b, a conductor 110 a, an insulator130 a, and a conductor 120 a. Here, the insulator 114 a and theinsulator 114 b correspond to the insulator 114, the insulator 140 a andthe insulator 140 b correspond to the insulator 140, the conductor 110 acorresponds to the conductor 110, the insulator 130 a corresponds to theinsulator 130, and the conductor 120 a corresponds to the conductor 120;therefore, for the details, the above description can be referred to.

In the capacitor 100 a, the insulator 114 b with a columnar shape andthe insulator 140 b are formed in an opening in the insulator 114 a andthe insulator 140 a. Also at the side surfaces of the columnar insulator114 b and the insulator 140 b, the conductor 110 a and the conductor 120a face each other with the insulator 130 a positioned therebetween.Accordingly, the capacitor 100 a can be formed not only at the sidesurfaces of the insulator 114 a and the insulator 140 a, but also at theside surfaces of the insulator 114 b and the insulator 140 b.Accordingly, the capacitance of the capacitor 100 a can be larger thanthat of the capacitor 100, while the area occupied by the 100 a issubstantially the same as that of the capacitor 100.

<Modification Example 3 of Semiconductor Device>

FIG. 15(A) and FIG. 15(B) are a top view and a cross-sectional view of asemiconductor device including a transistor 200 a and a transistor 200 bof one embodiment of the present invention.

In FIG. 15, FIG. 15(A) illustrates a top view. FIG. 15(B) is across-sectional view corresponding of a portion indicated by adashed-dotted line A1-A2 in FIG. 15(A) and also is a cross-sectionalview of the transistor 200 a and the transistor 200 b in a channellength direction. For clarity of the drawing, some components are notillustrated in the top view of FIG. 15(A).

In the semiconductor device illustrated in FIG. 15, the transistor 200 aand the transistor 200 b each have a similar structure to that of thetransistor 200 except that the conductor 205, the oxide 230 a, the oxide230 b, the oxide 243, the conductor 242, the conductor 240, theinsulator 241, and the conductor 246 are shared between the transistor200 a and the transistor 200 b. Thus, for the details, the abovedescription can be referred to.

As illustrated in FIGS. 15(A) and 15(B), when the transistor 200 a andthe transistor 200 b share the conductor 240, the area occupied by onetransistor element in the top view can be reduced; therefore, higherintegration of the semiconductor device can be achieved.

Note that although in this modification example, a structure where thetransistor 200 a includes a conductor 247 a and the transistor 200 bincludes a conductor 247 b is described, although, one embodiment of thepresent invention is not limited thereto. For example, a structure maybe employed where, as in the structure in FIG. 13, a capacitorelectrically connected to the transistor 200 a through the conductor 247a may be provided below the transistor 200 a, and a capacitorelectrically connected to the transistor 200 b through the conductor 247b may be provided below the transistor 200 b.

<Modification Example 4 of Semiconductor Device>

The semiconductor devices illustrated in FIG. 16 to FIG. 18 aresemiconductor devices including the transistor 200 with a differentshape from the transistor 200 illustrated in FIG. 1.

FIG. 16(A) is a top view of a semiconductor device including thetransistor 200. FIG. 16(B) and FIG. 16(C) are cross-sectional views ofthe semiconductor device. Here, FIG. 16(B) is a cross-sectional view ofa portion indicated by a dashed-dotted line A1-A2 in FIG. 16(A), and isa cross-sectional view of the transistor 200 in the channel lengthdirection In addition, FIG. 16(C) is a cross-sectional view of a portionindicated by a dashed-dotted line A3-A4 in FIG. 16(A), and is across-sectional view of the transistor 200 in the channel widthdirection. For clarity of the drawing, some components are notillustrated in the top view of FIG. 16(A). FIG. 17 is an enlarged viewof the vicinity of a channel formation region of the transistor 200 inFIG. 16(B). FIG. 18(A) is a cross-sectional view of a portion indicatedby a dashed-dotted line A5-A6 in FIG. 16(A), and is also across-sectional view in the channel width direction of a source regionor a drain region of the transistor 200. FIG. 18(B) is a cross-sectionalview of a portion indicated by a dashed-dotted line A7-A8 in FIG. 16(A),which corresponds to a cross-sectional view in the channel widthdirection of the conductor 240 b electrically connected to thetransistor 200 and functioning as a plug.

The semiconductor device illustrated in FIG. 16 and the like includesthe insulator 214 over a substrate (not illustrated), the transistor 200over the insulator 214, the insulator 280 over the transistor 200, theinsulator 282 over the insulator 280, the insulator 274 over theinsulator 282, and the insulator 281 over the insulator 274. Theinsulator 214, the insulator 280, the insulator 282, the insulator 274,and the insulator 281 function as interlayer films. The conductor 247functioning as a plug and electrically connected to the transistor 200is provided. In addition, the conductor 240 (the conductor 240 a and theconductor 240 b) that is electrically connected to the transistor 200and functions as a plug is preferably provided. Note that the insulator241 (the insulator 241 a and the insulator 241 b) is provided in contactwith the side surface of the conductor 240 functioning as a plug. Theconductor 246 (the conductor 246 a and the conductor 246 b) electricallyconnected to the conductor 240 and functioning as a wiring is providedover the insulator 281 and the conductor 240.

As illustrated in FIG. 16, the transistor 200 includes the insulator 216over the insulator 214; the conductor 205 (the conductor 205 a and theconductor 205 b) positioned so as to be embedded in the insulator 216;the insulator 222 over the insulator 216 and the conductor 205; theinsulator 224 over the insulator 222; the oxide 230 a over the insulator224; the oxide 230 b over the oxide 230 a; the oxide 243 a and the oxide243 b over the oxide 230 b; the conductor 242 a in contact with part ofthe top surface of the insulator 224, the side surface of the oxide 230a, the side surface of the oxide 230 b, the side surface of the oxide243 a, and the top surface of the oxide 243 a; the conductor 242 b incontact with part of the top surface of the insulator 224, the sidesurface of the oxide 230 a, the side surface of the oxide 230 b, theside surface of the oxide 243 b, and the top surface of the oxide 243 b;the oxide 230 c over the oxide 230 b; the insulator 250 over the oxide230 c; the conductor 260 (the conductor 260 a and the conductor 260 b)positioned over the insulator 250 and overlapping with the oxide 230 c;the insulator 272 in contact with part of the top surface of theinsulator 224, the side surface of the conductor 242 a, the top surfaceof the conductor 242 a, the side surface of the conductor 242 b, and thetop surface of the conductor 242 b; and the insulator 273 over theinsulator 272. The oxide 230 c is in contact with each of the sidesurface of the oxide 243 a, the top surface of an area of the oxide 243a that does not overlap with the conductor 242 a, the side surface ofthe oxide 243 b, and the top surface of an area of the oxide 243 b thatdoes not overlap with the conductor 242 b.

Here, the oxide 243 a includes the region that does not overlap with theconductor 242 a, and the oxide 243 b includes the region that does notoverlap with the conductor 242 b. That is, the oxide 243 a and the oxide243 b are provided so as to have a portion that projects into theopening provided in the insulator 280. In this regard, the transistor200 illustrated in FIG. 16 is different from the transistor illustratedin FIG. 1. For other structures of the semiconductor device illustratedin FIG. 16, corresponding structures illustrated in FIG. 1 can bereferred to.

FIG. 17 is an enlarged view of the vicinity of the channel formationregion of the transistor 200 in FIG. 16(B). As illustrated in FIG. 17,the side surfaces of the oxide 243 a and the oxide 243 b that face eachother are positioned in an inner side of the side surfaces of theconductor 242 a and the conductor 242 b that face each other. Thus, thedistance between a source electrode and a drain electrode of thetransistor 200, that is, the length of the channel length (L) isdetermined by the distance between the oxide 243 a and the oxide 243 b.The distance between the oxide 243 a and the oxide 243 b can be shorterthan the width of the opening provided in the insulator 280, and thanthe distance between the conductor 242 a and the conductor 242 b. Thatis, the opening provided in the insulator 280 can be formed large; thus,the oxide 230 c, the insulator 250, and the conductor 260 can beembedded easily in the opening even when the channel length of thetransistor 200 is provided to be short.

For example, in the case where the channel length (L) of the transistor200 is 20 nm, the width of the opening formed in the insulator 280 canbe 60 nm when the width of the region of the oxide 243 that does notoverlap with the conductor 242 can be 20 nm. Similarly, the width of theopening formed in the insulator 280 can be 30 nm when the width of theregion of the oxide 243 that does not overlap with the conductor 242 canbe 5 nm. In addition, part of the oxide 243 and part of the conductor260 can overlap with each other. Furthermore, in the case where thelength (L′) between the conductor 242 a and the conductor 242 billustrated in FIG. 17 is 60 nm, for example, the length of the channellength (L) can be less than 60 nm, preferably less than or equal to 30nm, more preferably greater than or equal to 5 nm and less than or equalto 10 nm.

Here, in the oxide 230 b, a region 234 functions as a channel formationregion, a region 231 a functions as one of a source region and a drainregion, and a region 231 b functions as the other of the source regionand the drain region.

FIG. 18(A) is a cross-sectional view of a portion indicated by adashed-dotted line A5-A6 in FIG. 16(A), and is also a cross-sectionalview in the channel width direction of a source region or a drain regionof the transistor 200. As illustrated in FIG. 18(A), a structure isemployed in which the top surface of the conductor 242 b and the sidesurface of the conductor 242 b are covered with the insulator 272 andthe insulator 273; thus, oxygen and impurities such as hydrogen andwater can be inhibited from being diffused into the conductor 242 b fromthe side surface direction of the conductor 242 b and the top surfacedirection of the conductor 242 b. Diffusion of oxygen from the peripheryof the conductor 242 b into the conductor 242 b can be inhibited, sothat the oxidation of the conductor 242 b can be inhibited. Note that asimilar effect can also be obtained with the conductor 242 a. Impuritiessuch as hydrogen and water can be inhibited from being diffused into theoxide 203 a and the oxide 230 b from the side surface direction of theoxide 230 a and the side surface direction of the oxide 230 b. For theinsulator 272, a silicon oxide film, a silicon nitride film or a siliconnitride oxide film can be used, for example. For the insulator 273,aluminum oxide or hafnium oxide can be used, for example.

FIG. 18(B) is a cross-sectional view of a portion indicated by adashed-dotted line A7-A8 in FIG. 16(A), which corresponds to across-sectional view in the channel width direction of the conductor 240b electrically connected to the transistor 200 and functioning as aplug. As illustrated in FIG. 18(B), the conductor 240 b is provided incontact with the top surface of the conductor 242 b. Since the insulator241 b is positioned at the side surface of the conductor 240 b, oxygenand impurities such as hydrogen and water from the insulator 280 can beprevented from diffusing into the conductor 240 b. Note that a similareffect can also be obtained with the conductor 240 a.

As illustrated in FIGS. 16(A) and 16(B) and FIG. 18(B), it is preferablethat the conductor 240 b be provided so as to overlap with at least partof the conductor 247. Accordingly, the area occupied by the conductor240 b and the conductor 247 in a top-view can be reduced; thus,miniaturization or higher integration of the semiconductor device ofthis embodiment can be achieved.

Next, a method for fabricating the semiconductor device including thetransistor 200 shown in FIG. 16 will be described with reference to FIG.19 to FIG. 23. In addition, (A) in each of FIG. 19 to FIG. 23 is a topview. Furthermore, (B) in each drawing is a cross-sectional viewcorresponding to a portion indicated by a dashed-dotted line A1-A2 in(A), and is also a cross-sectional view of the transistor 200 in thechannel length direction. Moreover, (C) in each drawing is across-sectional view corresponding to a portion indicated by adashed-dotted line A3-A4 in (A), and is also a cross-sectional view ofthe transistor 200 in the channel width direction. Note that forsimplification of the drawing, some components are not illustrated inthe top view of (A) in each drawing.

First, as described above, a fabrication process of the semiconductordevice is performed using the method illustrated in FIG. 4 to FIG. 6.

Next, the insulating film to be the insulator 280 is deposited over theinsulating film 273A. The insulating film to be the insulator 280 can bedeposited by a sputtering method, a CVD method, an MBE method, a PLDmethod, an ALD method, or the like. Next, the insulating film to be theinsulator 280 is subjected to CMP treatment, so that the insulator 280having a flat top surface is formed (see FIG. 19).

Then, part of the insulator 280, part of the insulating film 273A, partof the insulating film 272A, and part of the conductor layer 242B areprocessed to form an opening that exposes the oxide layer 243B. Theopening is preferably formed to overlap with the conductor 205. Theconductor 242 a, the conductor 242 b, the insulator 272, and theinsulator 273 are formed by forming the opening. Due to the formation ofthe opening, the thickness of part of the oxide layer 243B decreases insome cases (see FIG. 19).

Part of the insulator 280, part of the insulating film 273A, part of theinsulating film 272A, and part of the conductor layer 242B may beprocessed under different conditions. For example, part of the insulator280 may be processed by a dry etching method, part of the insulatingfilm 273A may be processed by a wet etching method, and part of theinsulating film 272A and part of the conductor layer 242B may beprocessed by a dry etching method.

Next, a dummy film 265A is formed over the insulator 280 and in theopening (see FIG. 20). The dummy film 265A needs to be deposited on asidewall of the opening; the distance between the oxide 243 a and theoxide 243 b, that is, the channel length (L) is determined by thethickness of the dummy film. Thus, the dummy film 265A is preferablydeposited by an ALD method or a CVD method that provides good coverageand makes fine adjustment of the thickness comparatively easily. Thedummy film 265A may be formed so as to have a thickness at the sidesurface of the opening of greater than or equal to 5 nm and less than orequal to 20 nm, and may be provided as appropriate depending onelectrical characteristics required for the transistor 200. For example,in the case where the thickness of the dummy film 265A at the sidewallof the opening is 5 nm, the channel length can be 10 nm shorter than thewidth of the opening; and in the case where the thickness of the dummyfilm 265A at the sidewall of the opening is 20 nm, the channel lengthcan be 40 nm shorter than the width of the opening. Note that it ispreferable to use a film that can be easily processed minutely andeasily removed as the dummy film 265A because the dummy film 265A isfinally removed.

Next, the dummy film 265A is subjected to anisotropic etching such thatonly a portion of the dummy film 265A in contact with the side surfaceof the opening remains, whereby a dummy film 265 is formed (see FIG.21). Here, the width of the dummy film 265 is preferably greater than orequal to 5 nm and less than or equal to 20 nm. The width of the dummyfilm 265 depends on the thickness of the dummy film 265A at the sidesurface of the opening. In the case where the width of the dummy film265 becomes short relative to the thickness of the dummy film 265A atthe side surface of the opening, the dummy film 265A can be formedthicker; therefore, the thickness of the dummy film 265A is not limitedto the value mentioned above.

Next, the oxide layer 243B is etched using the dummy film 265 as a mask,whereby the oxide 243 a and the oxide 243 b are formed (see FIG. 22).Note that etching of the dummy film 265 and etching of the oxide layer243B may be performed successively. Furthermore, in some cases, part ofthe top surface of the oxide 230 b that is exposed through the regionbetween the oxide 243 a and the oxide 243 b is removed.

At this time, the oxide layer 243B is processed using the dummy film 265as a mask, whereby the oxide 243 a and the oxide 243 b are formed. Thus,the opening formed in the insulator 280 overlaps with a region betweenthe conductor 242 a and the conductor 242 b and a region between theoxide 243 a and the oxide 243 b. In this manner, the conductor 260 canbe positioned between the conductor 242 a and the conductor 242 b andbetween the oxide 243 a and the oxide 243 b in a self-aligned manner ina later step.

In this embodiment, a method for forming the oxide layer 243B using thedummy film 265 is described; however, the method is not limited thereto.For example, the oxide 243 a and the oxide 243 b may be formed in such amanner that after the oxide layer 243B is formed, a resist mask or thelike is formed by performing patterning treatment, and the oxide layer243B is processed using the resist mask.

Then, the dummy film 265 is selectively removed using isotropic etching(see FIG. 23).

As the isotropic etching, wet etching or etching using a reactive gas isused, for example. In this manner, the distance between the oxide 243 aand the oxide 243 b can be shorter than the length of the opening in thechannel length direction.

In some cases, treatment such as dry etching performed in the aboveprocess causes the attachment or diffusion of impurities due to anetching gas or the like to a surface or an inside of the oxide 230 a,the oxide 230 b, or the like. Examples of the impurities includefluorine and chlorine.

In order to remove the impurities and the like, cleaning is performed.Examples of a cleaning method include wet cleaning using a cleaningsolution or the like, plasma treatment using plasma, and cleaning byheat treatment, and these cleanings may be performed in appropriatecombination.

As the wet cleaning, cleaning treatment may be performed using anaqueous solution obtained by diluting an oxalic acid, a phosphoric acid,ammonia water, a hydrofluoric acid, or the like with carbonated water orpure water. Alternatively, ultrasonic cleaning using pure water orcarbonated water may be performed.

As described above, the manufacturing process of the semiconductordevice can be performed using the method illustrated in FIG. 8 to FIG.11. In such a manner, the semiconductor device illustrated in FIG. 16can be fabricated. The structure, method, and the like described in theabove modification example can be used in combination as appropriatewith the other structures, methods, and the like described in thisembodiment.

The structure, method, and the like described above in this embodimentcan be used in combination as appropriate with the structures, methods,and the like described in the other embodiments.

Embodiment 2

In this embodiment, one embodiment of a semiconductor device will bedescribed with reference to FIG. 24 to FIG. 26.

[Memory Device 1]

FIG. 24 illustrates an example of a semiconductor device (memory device)in which the capacitor of one embodiment of the present invention isused. In the semiconductor device of one embodiment of the presentinvention, the transistor 200 is provided above a transistor 300, and acapacitor 100 is provided above the transistor 300 and the transistor200. Preferably, at least part of the capacitor 100 or the transistor300 overlaps with the transistor 200. Accordingly, the area occupied bythe capacitor 100, the transistor 200, and the transistor 300 in a topview can be reduced, whereby miniaturization or high integration of thesemiconductor device of this embodiment can achieved.

Note that the transistor 200 described in the above embodiment can beused as the transistor 200, and the capacitor 100 described in the aboveembodiment can be used as the capacitor 100. Therefore, for thetransistor 200, the capacitor 100, and layers including the transistor200 or the capacitor 100, the description in the above embodiment can bereferred to. Unlike in the above embodiment, the capacitor 100 isprovided over the transistor 200 in Memory device 1, which is differentfrom the above embodiment.

The transistor 200 is a transistor whose channel is formed in asemiconductor layer containing an oxide semiconductor. Since thetransistor 200 has a low off-state current, a memory device includingthe transistor 200 can retain stored data for a long time. In otherwords, such a memory device does not require refresh operation or has anextremely low frequency of the refresh operation, which leads to asufficient reduction in power consumption of the memory device.

In the memory device illustrated in FIG. 24, a wiring 1001 iselectrically connected to a source of the transistor 300, and a wiring1002 is electrically connected to a drain of the transistor 300. Awiring 1003 is electrically connected to one of the source and the drainof the transistor 200. A wiring 1004 is electrically connected to afirst gate of the transistor 200. A wiring 1006 is electricallyconnected to a second gate of the transistor 200. A gate of thetransistor 300 and the other of the source and the drain of thetransistor 200 are electrically connected to one electrode of thecapacitor 100. A wiring 1005 is electrically connected to the otherelectrode of the capacitor 100. Note that anode connected to the gate ofthe transistor 300, the other of the source and the drain of thetransistor 200, and the one electrode of the capacitor 100 ishereinafter referred to as a node FG in some cases.

The memory device illustrated in FIG. 24 is capable of data writing,retention, and reading by having a feature in that it is capable ofretaining the potential of the gate of the transistor 300 (the node FG)by switching of the transistor 200.

Furthermore, by arranging the memory devices illustrated in FIG. 24 in amatrix, a memory cell array can be formed.

<Transistor 300>

The transistor 300 is provided over a substrate 311 and includes aconductor 316 functioning as a gate electrode, an insulator 315functioning as a gate insulator, a semiconductor region 313 that is partof the substrate 311, and a low-resistance region 314 a and alow-resistance region 314 b functioning as a source region and a drainregion.

Here, the insulator 315 is positioned over the semiconductor region 313,and the conductor 316 is positioned over the insulator 315. Thetransistors 300 formed in the same layer are electrically isolated fromeach other by an insulator 312 functioning as an element isolationinsulating layer. The insulator 312 can be formed using an insulatorsimilar to that used for an insulator 326 or the like described later.The transistor 300 may be a p-channel transistor or an n-channeltransistor.

In the substrate 311, it is preferable that a region of thesemiconductor region 313 where a channel is formed, a region in thevicinity thereof, the low-resistance region 314 a and the low-resistanceregion 314 b functioning as the source region and the drain region, andthe like contain a semiconductor such as a silicon-based semiconductor;and it is also preferable that single crystal silicon is includedtherein. Alternatively, these regions may be formed using a materialcontaining Ge (germanium), SiGe (silicon germanium), GaAs (galliumarsenide), GaAlAs (gallium aluminum arsenide), or the like. A structuremay be employed in which silicon whose effective mass is controlled byapplying stress to the crystal lattice and thereby changing the latticespacing is used. Alternatively, the transistor 300 may be an HEMT (HighElectron Mobility Transistor) with GaAs and GaAlAs, or the like.

The low-resistance region 314 a and the low-resistance region 314 bcontain an element that imparts n-type conductivity, such as arsenic orphosphorus, or an element that imparts p-type conductivity, such asboron, in addition to the semiconductor material used for thesemiconductor region 313.

The conductor 316 functioning as a gate electrode can be formed using asemiconductor material such as silicon containing an element thatimparts n-type conductivity, such as arsenic or phosphorus, or anelement that imparts p-type conductivity, such as boron, or using aconductive material such as a metal material, an alloy material, or ametal oxide material.

Note that the work function depends on a material of the conductor,thus, the threshold voltage can be adjusted by changing the material ofthe conductor. Specifically, it is preferable to use a material such astitanium nitride or tantalum nitride for the conductor. Moreover, inorder to ensure both conductivity and embeddability, it is preferable touse stacked layers of metal materials such as tungsten and aluminum forthe conductor, and it is particularly preferable to use tungsten interms of heat resistance.

Here, in the transistor 300 illustrated in FIG. 24, the semiconductorregion 313 (part of the substrate 311) in which a channel is formed hasa convex shape. Furthermore, the conductor 316 is provided so as tocover a side surface and top surface of the semiconductor region 313with the insulator 315 positioned therebetween. Such a transistor 300 isalso referred to as a FIN-type transistor because it utilizes a convexportion of the semiconductor substrate. Note that an insulatorfunctioning as a mask for forming the convex portion may be placed incontact with an upper portion of the convex portion. Furthermore,although the case where the convex portion is formed by processing partof the semiconductor substrate is described here, a semiconductor filmhaving a convex shape may be formed by processing an SOI substrate.

Note that the transistor 300 illustrated in FIG. 24 is only an exampleand is not limited to the structure illustrated therein; an appropriatetransistor may be used in accordance with a circuit structure or adriving method.

<Wiring Layers>

Wiring layers provided with an interlayer film, a wiring, a plug, andthe like may be provided between the components. A plurality of wiringlayers can be provided in accordance with the design. Note that aplurality of conductors functioning as plugs or wirings are collectivelydenoted by the same reference numeral in some cases. Furthermore, inthis specification and the like, a wiring and a plug electricallyconnected to the wiring may be a single component. That is, there are acase where part of a conductor functions as a wiring and a case wherepart of a conductor functions as a plug.

For example, an insulator 320, an insulator 322, an insulator 324, andan insulator 326 are sequentially stacked over the transistor 300 asinterlayer films. In addition, A conductor 328, a conductor 330, and thelike that are electrically connected to the capacitor 100 or thetransistor 200 are embedded in the insulator 320, the insulator 322, theinsulator 324, and the insulator 326. Note that the conductor 328 andthe conductor 330 function as plugs or wirings.

The insulator functioning as an interlayer film may function as aplanarization film that covers an uneven shape thereunder. For example,a top surface of the insulator 322 may be planarized by planarizationtreatment using a chemical mechanical polishing (CMP) method or the liketo improve planarity.

A wiring layer may be provided over the insulator 326 and the conductor330. For example, in FIG. 24, an insulator 350, an insulator 352, and aninsulator 354 are stacked in this order. Furthermore, a conductor 356 isformed in the insulator 350, the insulator 352, and the insulator 354.The conductor 356 functions as a plug or a wiring.

Similarly, a conductor 247, a conductor included in the transistor 200(the conductor 205), and the like are embedded in an insulator 210, aninsulator 212, the insulator 214, an insulator 216, an insulator 222,and an insulator 224. Note that the conductor 247 has a function of aplug or a wiring that is electrically connected to the capacitor 100,the transistor 200, or the transistor 300. For example, the conductor247 is electrically connected to the conductor 316 functioning as thegate electrode of the transistor 300.

A conductor 112, conductors included in the capacitor 100 (the conductor120 and the conductor 110) and the like are embedded in the insulator114, the insulator 140, the insulator 130, the insulator 150, and aninsulator 154 over the insulator 281. Note that the conductor 112functions as a plug or a wiring that electrically connects thetransistor 200 or the transistor 300 and a conductor 152 functioning asa terminal. An insulator 156 is provided over the insulator 154 and theconductor 152.

Examples of an insulator that can be used as an interlayer film includean oxide, a nitride, an oxynitride, a nitride oxide, a metal oxide, ametal oxynitride, and a metal nitride oxide, each of which has aninsulating property.

For example, when a material having a low relative permittivity is usedfor the insulator functioning as an interlayer film, the parasiticcapacitance generated between wirings can be reduced. Thus, a materialis preferably selected depending on the function of the insulator.

For example, for the insulator 320, the insulator 322, the insulator326, the insulator 352, the insulator 354, the insulator 212, theinsulator 114, the insulator 150, the insulator 156, and the like, aninsulator with low relative permittivity is preferably used. Forexample, the insulator preferably includes silicon oxide, siliconoxynitride, silicon nitride oxide, silicon nitride, silicon oxide towhich fluorine is added, silicon oxide to which carbon is added, siliconoxide to which carbon and nitrogen are added, porous silicon oxide, aresin, or the like. Alternatively, the insulators each preferably have astacked-layer structure of a resin and silicon oxide, siliconoxynitride, silicon nitride oxide, silicon nitride, silicon oxide towhich fluorine is added, silicon oxide to which carbon is added, siliconoxide to which carbon and nitrogen are added, or porous silicon oxide.When silicon oxide or silicon oxynitride, which is thermally stable, iscombined with a resin, the stacked-layer structure can have thermalstability and a low relative permittivity. Examples of the resin includepolyester, polyolefin, polyamide (nylon, aramid, or the like),polyimide, polycarbonate, and acrylic.

It is preferable that the resistivity of an insulator provided over orunder the conductor 152 be higher than or equal to 1.0×10¹² Ωcm andlower than or equal to 1.0×10¹⁵ Ωcm, preferably higher than or equal to5.0×10¹² Ωcm and lower than or equal to 1.0×10¹⁴ Ωcm, further preferablyhigher than or equal to 1.0×10¹³ Ωcm and lower than or equal to 5.0×10¹³Ωcm. When the resistivity of the insulator provided over or under theconductor 152 is within the above range, the insulator can dispersecharge accumulated between the transistor 200, the transistor 300, thecapacitor 100, the conductor 152, and the like and can inhibit poorcharacteristics and electrostatic breakdown of the transistor and amemory device including the transistor due to the charge, whilemaintaining the insulating property. For such an insulator, siliconnitride or silicon nitride oxide can be used. For example, theresistivity of the insulator 154 can be set within the above range.

When the transistor using an oxide semiconductor is surrounded by aninsulator that has a function of inhibiting the transmission of oxygenand impurities such as hydrogen, the electrical characteristics of thetransistor can be stable. Thus, an insulator having a function ofinhibiting the transmission of oxygen and impurities such as hydrogen isused as the insulator 324, the insulator 350, the insulator 210, and theinsulator 154.

As an insulator having a function of inhibiting the transmission ofoxygen and impurities such as hydrogen, a single layer or a stackedlayer of an insulator containing, for example, boron, carbon, nitrogen,oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, chlorine,argon, gallium, germanium, yttrium, zirconium, lanthanum, neodymium,hafnium, or tantalum is used. Specifically, as the insulator having afunction of inhibiting the transmission of oxygen and impurities such ashydrogen, a metal oxide such as aluminum oxide, magnesium oxide, galliumoxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide,neodymium oxide, hafnium oxide, or tantalum oxide; silicon nitrideoxide; or silicon nitride can be used.

For the conductors that can be used as a wiring or a plug, a materialcontaining one or more kinds of metal elements selected from aluminum,chromium, copper, silver, gold, platinum, tantalum, nickel, titanium,molybdenum, tungsten, hafnium, vanadium, niobium, manganese, magnesium,zirconium, beryllium, indium, ruthenium, and the like can be used. Asemiconductor having high electrical conductivity, typified bypolycrystalline silicon containing an impurity element such asphosphorus, or silicide such as nickel silicide may be used.

For example, for the conductor 328, the conductor 330, the conductor356, the conductor 247, the conductor 112, the conductor 152 or thelike, a single layer or stacked layers of a conductive material such asa metal material, an alloy material, a metal nitride material, or ametal oxide material that is formed using the above material can beused. It is preferable to use a high-melting-point material that hasboth heat resistance and conductivity, such as tungsten or molybdenum,and it is particularly preferable to use tungsten. Alternatively, alow-resistance conductive material such as aluminum or copper ispreferably used. The use of a low-resistance conductive material canreduce wiring resistance.

<Wiring or Plug in Layer Provided with Oxide Semiconductor>

In the case where an oxide semiconductor is used in the transistor 200,an insulator including an excess oxygen region is provided in thevicinity of the oxide semiconductor in some cases. In that case, aninsulator having a barrier property is preferably provided between theinsulator including the excess oxygen region and the conductor providedin the insulator including the excess oxygen region.

For example, an insulator 276 is preferably provided between theinsulator 280 including excess oxygen and a conductor 245 in FIG. 24.Here, the conductor 245 corresponds to the conductor 240 described inthe above embodiment and the insulator 276 corresponds to the insulator241 described in the above embodiment. Since the insulator 276 isprovided in contact with the insulator 272, the conductor 245 and thetransistor 200 can be scaled by the insulators having a barrierproperty.

That is, the excess oxygen included in the insulator 280 can beinhibited from being absorbed by the conductor 245 when the insulator276 is provided. In addition, diffusion of hydrogen, which is animpurity, into the transistor 200 through the conductor 245 can beinhibited when the insulator 276 is included.

Here, the conductor 245 functions as a plug or a wiring that iselectrically connected to the capacitor 100, the transistor 200, or thetransistor 300. For example, the conductor 245 electrically connects theconductor 242 b functioning as the other of the source and the drain ofthe transistor 200 and the conductor 110 functioning as one of theelectrodes of the capacitor 100 through the conductor 246.

The above is the description of the structure example. With the use ofthe structure, a change in electrical characteristics can be reduced andreliability can be improved in a semiconductor device using a transistorincluding an oxide semiconductor. Alternatively, a transistor includingan oxide semiconductor and having high on-state current can be provided.

Alternatively, a transistor including an oxide semiconductor and havinglow off-state current can be provided. Alternatively, a semiconductordevice with low power consumption can be provided.

[Memory Device 2]

FIG. 25 illustrates an example of a memory device using thesemiconductor device of one embodiment of the present invention. Likethe semiconductor device illustrated in FIG. 24, the memory deviceillustrated in FIG. 25 includes the transistor 200, the transistor 300,and the capacitor 100. Note that the memory device illustrated in FIG.25 is different from the memory device illustrated in FIG. 24 in thatthe capacitor 100 is positioned under the transistor 200 and thetransistor 200 and the transistor 300 are not electrically connected toeach other through the conductor 247.

In the semiconductor device of one embodiment of the present invention,the transistor 200 is provided above the transistor 300, and thecapacitor 100 is provided below the transistor 200. Preferably, at leastpart of the capacitor 100 or the transistor 300 overlaps with thetransistor 200. In such cases, the area occupied by the capacitor 100,the transistor 200, and the transistor 300 in the top view can bereduced, whereby the semiconductor device of this embodiment can beminiaturized or highly integrated.

Note that the capacitor 100, the transistor 200, and the transistor 300mentioned above can be used as the capacitor 100, the transistor 200,and the transistor 300, respectively. Therefore, the above descriptioncan be referred to for the capacitor 100, the transistor 200, thetransistor 300, and the layers including the capacitor 100, thetransistor 200, or the transistor 300.

In the memory device illustrated in FIG. 25, a wiring 2001 iselectrically connected to the source of the transistor 300, a wiring2002 is electrically connected to the drain of the transistor 300, and awiring 2007 is electrically connected to the gate of the transistor 300.A wiring 2003 is electrically connected to one of the source and thedrain of the transistor 300, a wiring 2004 is electrically connected toa first gate of the transistor 200, and a wiring 2006 is electricallyconnected to a second gate of the transistor 200. The other of thesource and the drain of the transistor 200 is electrically connected toone of the electrodes of the capacitor 100, and a wiring 2005 iselectrically connected to the other electrode of the capacitor 100.

The memory device illustrated in FIG. 25 has characteristics of beingable to retain charge stored in one of the electrodes of the capacitor100 by switching of the transistor 200; thus, writing, retention, andreading of data can be performed.

Furthermore, by arranging the memory devices illustrated in FIG. 25 in amatrix, a memory cell array can be formed.

The layer including the transistor 300 has the same structure as that inthe memory device illustrated in FIG. 24, and therefore the abovedescription can be referred to for the structure below the insulator354.

An insulator 360 is positioned over the insulator 354, an insulator 362is positioned over the insulator 360, an insulator 364 is positionedover the insulator 362, and an insulator 114 is positioned over theinsulator 364. An insulator that can be used as the insulator 350 andthe like can be used as the insulator 360. For the insulator 362 and theinsulator 364, an insulator that can be used for the insulator 352 orthe like can be used.

An opening is formed in the insulator 364, and a conductor 366 ispositioned in the opening. The conductor 366 is in contact with thebottom surface of the conductor 110. That is, the conductor 366functions as a wiring that connects to the other electrode of thecapacitor 100. For the conductor 366, an insulator that can be used forthe conductor 356 and the like can be used.

The conductor 112, conductors included in the capacitor 100 (theconductor 120 and the conductor 110), and the like are embedded in theinsulator 360, the insulator 362, the insulator 364, the insulator 114,the insulator 140, the insulator 130, and the insulator 150. Note thatthe conductor 112 functions as a plug or a wiring that electricallyconnects the transistor 300 and the conductor 152 that functions as aterminal.

The layer over the insulator 150 including the transistor 200 has thesame structure as that in the memory device illustrated in FIG. 24;therefore, the above description can be referred to. However, thetransistor 200 in the memory device illustrated in FIG. 25 does notinclude the conductor 240 b. Furthermore, the conductor 152 ispositioned over the conductor 245, and the insulator 156 is positionedover the conductor 152 and the insulator 281.

The conductor 247 functions as a plug or a wiring that is electricallyconnected to the capacitor 100, the transistor 200, or the transistor300. For example, the conductor 247 is electrically connected to theconductor 120 functioning as the other electrode of the capacitor 100.

[Memory Device 3]

FIG. 26 illustrates an example of a memory device using thesemiconductor device of one embodiment of the present invention. Thememory device illustrated in FIG. 26 includes the transistor 400 inaddition to the semiconductor device including the transistor 200, thetransistor 300, and the capacitor 100 illustrated in FIG. 24.

The transistor 400 can control a second gate voltage of the transistor200. For example, a first gate and a second gate of the transistor 400are diode-connected to a source of the transistor 400, and the sourcethereof is connected to the second gate of the transistor 200. When anegative potential of the second gate of the transistor 200 is retainedin this structure, the first gate-source voltage and the secondgate-source voltage of the transistor 400 are 0 V. In the transistor400, a drain current when the second gate voltage and the first gatevoltage are 0 V is extremely low; thus, the negative potential of thesecond gate of the transistor 200 can be held for a long time evenwithout power supply to the transistor 200 and the transistor 400.Accordingly, the memory device including the transistor 200 and thetransistor 400 can retain stored data for a long time.

Hence, in FIG. 26, the wiring 1001 is electrically connected to thesource of the transistor 300, and the wiring 1002 is electricallyconnected to the drain of the transistor 300. The wiring 1003 iselectrically connected to one of the source and the drain of thetransistor 200, the wiring 1004 is electrically connected to the gate ofthe transistor 200, and the wiring 1006 is electrically connected to aback gate of the transistor 200. A gate of the transistor 300 and theother of the source and the drain of the transistor 200 are electricallyconnected to one of the electrodes of the capacitor 100. The wiring 1005is electrically connected to the other electrode of the capacitor 100. Awiring 1007 is electrically connected to the source of the transistor400, a wiring 1008 is electrically connected to a gate of the transistor400, a wiring 1009 is electrically connected to a back gate of thetransistor 400, and a wiring 1010 is electrically connected to the drainof the transistor 400. The wiring 1006, the wiring 1007, the wiring1008, and the wiring 1009 are electrically connected to each other.

When the memory devices illustrated in FIG. 26 are arranged in a matrixlike the memory devices illustrated in FIG. 24, a memory cell array canbe formed. Note that one transistor 400 can control second gate voltagesof the transistors 200. For this reason, the number of providedtransistors 400 is preferably smaller than the number of transistors200.

Note that in the memory device illustrated in FIG. 24, the capacitor 100is a cylinder shape; however, the present invention is not limitedthereto. For example, as illustrated in FIG. 26, the capacitor 100 maybe a planar shape.

<Transistor 400>

The transistor 400 and the transistors 200 are formed in the same layerand thus can be fabricated in parallel. The transistor 400 includes aconductor 460 (a conductor 460 a and a conductor 460 b) functioning as afirst gate electrode; a conductor 405 (a conductor 405 a and a conductor405 b) functioning as a second gate electrode; the insulator 222, theinsulator 224, and an insulator 450 each functioning as a gateinsulating layer, an oxide 430 c including a region where a channel isformed; a conductor 442 a functioning as one of a source and a drain; anoxide 443 a, an oxide 431 a, and an oxide 431 b; a conductor 442 bfunctioning as the other of the source and the drain; an oxide 443 b, anoxide 432 a and an oxide 432 b; and a conductor 440 (a conductor 440 aand a conductor 440 b).

In the transistor 400, the conductor 405 is in the same layer as theconductor 205. The oxide 431 a and the oxide 432 a are in the same layeras the oxide 230 a, and the oxide 431 b and the oxide 432 b are in thesame layer as the oxide 230 b. The conductor 442 is in the same layer asthe conductor 242. The oxide 443 is in the same layer as the oxide 243.The oxide 430 c is in the same layer as the oxide 230 c. The insulator450 is in the same layer as the insulator 250. The conductor 460 is inthe same layer as the conductor 260.

Note that the structure bodies formed in the same layer can be formed atthe same time. For example, the oxide 430 c can be formed by processingan oxide film to be the oxide 230 c.

In the oxide 430 c functioning as an active layer of the transistor 400,oxygen vacancies and impurities such as hydrogen and water are reduced,as in the oxide 230 or the like.

Accordingly, the threshold voltage of the transistor 400 can be higherthan 0 V, an off-state current can be reduced, and the drain current atthe time when the second gate voltage and the first gate voltage are 0 Vcan be extremely low.

<Dicing Line>

A dicing line (also referred to as a scribe line, a dividing line, or acutting line in some cases) that is provided when a large-sizedsubstrate is divided into semiconductor elements so that a plurality ofsemiconductor devices are each formed in a chip form will be describedbelow. Examples of a dividing method include the case where a groove (adicing line) for dividing the semiconductor elements is formed on thesubstrate, and then the substrate is cut along the dicing line to divide(split) it into a plurality of semiconductor devices.

Here, for example, as illustrated in FIG. 26, it is preferable that aregion in which the insulator 272 and the insulator 222 are in contactwith each other be the dicing line. That is, an opening is provided inthe insulator 224 near the region to be the dicing line that is providedin the outer edge of the transistor 400 and the memory cell including aplurality of transistors 200. The insulator 272 is provided to cover theside surface of the insulator 224.

That is, in the opening provided in the insulator 224, the insulator 222is in contact with the insulator 272. For example, the insulator 222 andthe insulator 272 may be formed using the same material and the samemethod. When the insulator 222 and the insulator 272 are formed usingthe same material and the same method, the adhesion therebetween can beincreased. For example, aluminum oxide is preferably used.

With such a structure, the insulator 224, the transistor 200, and thetransistor 400 can be enclosed with the insulator 222 and the insulator272. Since the insulator 222 and the insulator 272 have a function ofinhibiting diffusion of oxygen, hydrogen, and water even when thesubstrate is divided into circuit regions each of which is provided withthe semiconductor elements in this embodiment to form a plurality ofchips, the entry and diffusion of impurities such as hydrogen or waterfrom the direction of a side surface of the divided substrate to thetransistor 200 or the transistor 400 can be inhibited.

In the structure, excess oxygen in the insulator 224 can be inhibitedfrom diffusing into the outside of the insulator 272 and the insulator222. Accordingly, excess oxygen in the insulator 224 is efficientlysupplied to the oxide where the channel is formed in the transistor 200or the transistor 400. The oxygen can reduce oxygen vacancies in theoxide where the channel is formed in the transistor 200 or thetransistor 400. Thus, the oxide where the channel is formed in thetransistor 200 or the transistor 400 can be an oxide semiconductor witha low density of defect states and stable characteristics. That is, achange in electrical characteristics of the transistors 200 or thetransistor 400 can be inhibited and reliability can be improved.

This embodiment can be implemented in combination with any of thestructures described in the other embodiments and the like, asappropriate.

Embodiment 3

In this embodiment, a memory device of one embodiment of the presentinvention including a transistor in which an oxide is used for asemiconductor (hereinafter referred to as an OS transistor in somecases) and a capacitor (hereinafter such a memory device is alsoreferred to as an OS memory device in some cases) will be described withreference to FIG. 27 and FIG. 28. The OS memory device includes at leasta capacitor and an OS transistor that controls the charging anddischarging of the capacitor. Since the OS transistor has an extremelylow off-state current, the OS memory device has excellent retentioncharacteristics and thus can function as a nonvolatile memory.

<Structure Example of Memory Device>

FIG. 27(A) illustrates a structure example of the OS memory device. Amemory device 1400 includes a peripheral circuit 1411 and a memory cellarray 1470. The peripheral circuit 1411 includes a row circuit 1420, acolumn circuit 1430, an output circuit 1440, and a control logic circuit1460.

The column circuit 1430 includes, for example, a column decoder, aprecharge circuit, a sense amplifier, a write circuit, and the like. Theprecharge circuit has a function of precharging wirings. The senseamplifier has a function of amplifying a data signal read from a memorycell. Note that the wirings are connected to the memory cell included inthe memory cell array 1470, and will be described later in detail. Theamplified data signal is output as a data signal RDATA to the outside ofthe memory device 1400 through the output circuit 1440. The row circuit1420 includes, for example, a row decoder and a word line drivercircuit, and can select a row to be accessed.

As power supply voltages from the outside, a low power supply voltage(VSS), a high power supply voltage (VDD) for the peripheral circuit1411, and a high power supply voltage (VIL) for the memory cell array1470 are supplied to the memory device 1400. Control signals (CE, WE,and RE), an address signal ADDR, and a data signal WDATA are also inputto the memory device 1400 from the outside. The address signal ADDR isinput to the row decoder and the column decoder, and WDATA is input tothe write circuit.

The control logic circuit 1460 processes the signals (CE, WE, and RE)input from the outside, and generates control signals for the rowdecoder and the column decoder. CE denotes a chip enable signal, WEdenotes a write enable signal, and RB denotes a read enable signal.Signals processed by the control logic circuit 1460 are not limitedthereto, and other control signals may be input as necessary.

The memory cell array 1470 includes a plurality of memory cells MC and aplurality of wirings arranged in a matrix. Note that the number of thewirings that connect the memory cell array 1470 to the row circuit 1420depends on the structure of the memory cell MC, the number of the memorycells MC in a column, and the like. The number of the wirings thatconnect the memory cell array 1470 to the column circuit 1430 depends onthe structure of the memory cell MC, the number of the memory cells MCin a row, and the like.

Note that FIG. 27(A) illustrates an example in which the peripheralcircuit 1411 and the memory cell array 1470 are formed on the sameplane; however, this embodiment is not limited thereto. For example, asillustrated in FIG. 27(B), the memory cell army 1470 may be providedover the peripheral circuit 1411 to partly overlap with the peripheralcircuit 1411. For example, the sense amplifier may be provided below thememory cell array 1470 so that they overlap with each other.

FIG. 28 illustrate structure examples of memory cells applicable to thememory cell MC.

[DOSRAM]

FIG. 28(A) to FIG. 28(C) each illustrate a circuit structure example ofa DRAM memory cell. In this specification and the like, a DRAM using amemory cell including one OS transistor and one capacitor is sometimesreferred to as a DOSRAM (Dynamic Oxide Semiconductor Random AccessMemory). A memory cell 1471 illustrated in FIG. 28(A) includes atransistor M1 and a capacitor CA. Note that the transistor M1 includes agate (also referred to as a front gate in some cases) and a back gate.

A first terminal of the transistor M1 is connected to a first terminalof the capacitor CA. A second terminal of the transistor M1 is connectedto a wiring BIL. Agate of the transistor M1 is connected to a wiringWOL. Aback gate of the transistor M1 is connected to a wiring BGL. Asecond terminal of the capacitor CA is connected to a wiring CAL.

The wiring BIL functions as a bit line, and the wiring WOL functions asa word line. The wiring CAL functions as a wiring for applying apredetermined potential to the second terminal of the capacitor CA. Inthe time of data writing and data reading, a low-level potential ispreferably applied to the wiring CAL. The wiring BGL functions as awiring for applying a potential to the back gate of the transistor M1.By applying a given potential to the wiring BGL, the threshold voltageof the transistor M1 can be increased or decreased.

Here, the memory cell 1471 illustrated in FIG. 28(A) corresponds to thememory device illustrated in FIG. 25. That is, the transistor M1, thecapacitor CA, the wiring BIL, the wiring WOL, the wiring BGL, and thewiring CAL correspond to the transistor 200, the capacitor 100, thewiring 2003, the wiring 2004, the wiring 2006, and the wiring 2005,respectively. Note that the transistor 300 illustrated in FIG. 25corresponds to a transistor provided in the peripheral circuit 1411 ofthe memory device 1400 illustrated in FIG. 27(B).

The memory cell MC is not limited to the memory cell 1471, and thecircuit structure can be changed. For example, in the memory cell MC,the back gate of the transistor M1 may be connected to the wiring WOLinstead of the wiring BGL as in a memory cell 1472 illustrated in FIG.28(B). As another example, the memory cell MC may be configured with asingle-gate transistor, that is, the transistor M1 that does not have aback gate, like a memory cell 1473 illustrated in FIG. 28(C).

In the case where the semiconductor device described in the aboveembodiment is used in the memory cell 1471 or the like, the transistor200 can be used as the transistor M1, and the capacitor 100 can be usedas the capacitor CA. The use of an OS transistor as the transistor M1enables the leakage current of the transistor M1 to be extremely low.That is, written data can be retained for a long time with thetransistor M1; thus, the frequency of refresh of the memory cell can bereduced. Alternatively, the refresh operation of the memory cell can beomitted. In addition, the extremely low leakage current allowsmulti-level data or analog data to be retained in the memory cell 1471,the memory cell 1472, or the memory cell 1473.

In addition, in the DOSRAM, when the sense amplifier is provided belowthe memory cell array 1470 to overlap with the memory cell array 1470 asdescribed above, the bit line can be shortened. This reduces bit linecapacity, which reduces the storage capacity of the memory cell.

[NOSRAM]

FIGS. 28(D) to 28(H) each illustrate a circuit structure example of again-cell memory cell including two transistors and one capacitor. Amemory cell 1474 illustrated in FIG. 28(D) includes a transistor M2, atransistor M3, and a capacitor CB. Note that the transistor M2 includesa front gate (simply referred to as a gate in some cases) and a backgate. In this specification and the like, a memory device including again-cell memory cell using an OS transistor as the transistor M2 isreferred to as a NOSRAM (Nonvolatile Oxide Semiconductor RAM) in somecases.

A first terminal of the transistor M2 is connected to a first terminalof the capacitor CB. A second terminal of the transistor M2 is connectedto a wiring WBL. The gate of the transistor M2 is connected to thewiring WOL. The back gate of the transistor M2 is connected to thewiring BGL. A second terminal of the capacitor CB is connected to thewiring CAL. A first terminal of the transistor M3 is connected to thewiring RBL, a second terminal of the transistor M3 is connected to thewiring SL, and a gate of the transistor M3 is connected to the firstterminal of the capacitor CB.

The wiring WBL functions as a write bit line. The wiring RBL functionsas a read bit line. The wiring WOL functions as a word line. The wiringCAL functions as a wiring for applying a predetermined potential to thesecond terminal of the capacitor CB. During data writing, dataretention, and data reading, a low-level potential is preferably appliedto the wiring CAL. The wiring BGL functions as a wiring for applying apotential to the back gate of the transistor M2. By applying a givenpotential to the wiring BGL, the threshold voltage of the transistor M2can be increased or decreased.

Here, the memory cell 1474 illustrated in FIG. 28(D) corresponds to thememory device illustrated in FIG. 24. That is, the transistor M2, thecapacitor CB, the transistor M3, the wiring WBL, the wiring WOL, thewiring BGL, the wiring CAL, the wiring RBL, and the wiring SL correspondto the transistor 200, the capacitor 100, the transistor 300, the wiring1003, the wiring 1004, the wiring 1006, the wiring 1005, the wiring1002, and the wiring 1001, respectively.

In addition, the memory cell MC is not limited to the memory cell 1474,and the circuit structure can be changed as appropriate. For example, asin a memory cell 1475 illustrated in FIG. 28(E), a structure may beemployed in which the back gate of the transistor M2 is connected not tothe wiring BGL but to the wiring WOL in the memory cell MC.Alternatively, for example, like a memory cell 1476 illustrated in FIG.28(F), the memory cell MC may be a memory cell including a single-gatetransistor, that is, the transistor M2 that does not include a backgate. Alternatively, for example, like a memory cell 1477 illustrated inFIG. 28(G), the memory cell MC may have a structure where the wiring WBLand the wiring RBL are combined into one wiring BIL.

In the case where the semiconductor device described in the aboveembodiment is used in the memory cell 1474 or the like, the transistor200 can be used as the transistor M2, the transistor 300 can be used asthe transistor M3, and the capacitor 100 can be used as the capacitorCB. When an OS transistor is used as the transistor M2, the leakagecurrent of the transistor M2 can be extremely low. Consequently, writtendata can be retained for a long time with the transistor M2; thus, thefrequency of refresh of the memory cell can be reduced. Alternatively,the refresh operation of the memory cell can be omitted. In addition,the extremely low leakage current allows multi-level data or analog datato be retained in the memory cell 1474. The same applies to the memorycells 1475 to 1477.

Note that the transistor M3 may be a transistor containing silicon in achannel formation region (hereinafter such a transistor is referred toas a Si transistor in some cases). The conductivity type of the Sitransistor may be either an n-channel type or a p-channel type. A Sitransistor has higher field-effect mobility than an OS transistor insome cases. Therefore, a Si transistor may be used as the transistor M3functioning as a read transistor. Furthermore, the use of a Sitransistor as the transistor M3 enables the transistor M2 to be stackedover the transistor M3, in which case the area occupied by the memorycell can be reduced and high integration of the memory device can beachieved.

Alternatively, the transistor M3 may be an OS transistor. When OStransistors are used as the transistors M2 and M3, the circuit of thememory cell array 1470 can be formed using only n-channel transistors.

In addition, FIG. 28(H) illustrates an example of a gain-cell memorycell including three transistors and one capacitor. A memory cell 1478illustrated in FIG. 28(H) includes transistors M4 to M6 and a capacitorCC. The capacitor CC is provided as appropriate. The memory cell 1478 iselectrically connected to wirings BIL, RWL, WWL, BGL, and GNDL. Thewiring GNDL is a wiring for supplying a low-level potential. Note thatthe memory cell 1478 may be electrically connected to the wirings RBLand WBL instead of the wiring BIL.

The transistor M4 is an OS transistor including a back gate, and theback gate is electrically connected to the wiring BGL. Note that theback gate and a gate of the transistor M4 may be electrically connectedto each other. Alternatively, the transistor M4 does not necessarilyinclude the back gate.

Note that each of the transistors M5 and M6 may be an n-channel Sitransistor or a p-channel Si transistor. Alternatively, the transistorsM4 to M6 may be OS transistors, in which case the circuit of the memorycell army 1470 can be formed using only n-channel transistors.

In the case where the semiconductor device described in the aboveembodiment is used in the memory cell 1478, the transistor 200 can beused as the transistor M4, the transistors 300 can be used as thetransistors M5 and M6, and the capacitor 100 can be used as thecapacitor CC. The use of an OS transistor as the transistor M4 enablesthe leakage current of the transistor M4 to be extremely low.

Note that the structures of the peripheral circuit 1411, the memory cellarray 1470, and the like described in this embodiment are not limited tothose described above. The arrangement and functions of these circuitsand the wirings, circuit components, and the like connected to thecircuits can be changed, removed, or added as needed.

The structure described in this embodiment can be used in an appropriatecombination with the structures described in the other embodiments andthe like.

Embodiment 4

In this embodiment, an example of a chip 1200 on which the semiconductordevice of the present invention is mounted will be described withreference to FIG. 29 A plurality of circuits (systems) are implementedin the chip 1200. A technique for integrating a plurality of circuits(systems) into one chip is referred to as system on chip (SoC) in somecases.

As illustrated in FIG. 29(A), the chip 1200 includes a CPU (CentralProcessing Unit) 1211, a GPU (Graphics Processing Unit) 1212, one ormore of analog arithmetic units 1213, one or more of memory controllers1214, one or more of interfaces 1215, one or more of network circuits1216, and the like.

A bump (not illustrated) is provided on the chip 1200, and asillustrated in FIG. 29(B), the chip 1200 is connected to a first surfaceof a printed circuit board (PCB) 1201. In addition, a plurality of bumps1202 are provided on a rear side of the first surface of the PCB 1201,and the PCB 1201 is connected to a motherboard 1203.

Memory devices such as DRAMs 1221 and a flash memory 1222 may beprovided over the motherboard 1203. For example, the DOSRAM described inthe above embodiment can be used as the DRAM 1221. In addition, forexample, the NOSRAM described in the above embodiment can be used as theflash memory 1222.

The CPU 1211 preferably includes a plurality of CPU cores. In addition,the GPU 1212 preferably includes a plurality of GPU cores. Furthermore,the CPU 1211 and the GPU 1212 may each include a memory for temporarilystoring data. Alternatively, a common memory for the CPU 1211 and theGPU 1212 may be provided in the chip 1200. The NOSRAM or the DOSRAMdescribed above can be used as the memory. Moreover, the GPU 1212 issuitable for parallel computation of a number of data and thus can beused for image processing or product-sum operation. When an imageprocessing circuit or a product-sum operation circuit using an oxidesemiconductor of the present invention is provided in the GPU 1212,image processing and product-sum operation can be performed with lowpower consumption.

In addition, since the CPU 1211 and the GPU 1212 are provided on thesame chip, a wiring between the CPU 1211 and the GPU 1212 can beshortened, and the data transfer from the CPU 1211 to the GPU 1212, thedata transfer between the memories included in the CPU 1211 and the GPU1212, and the transfer of arithmetic operation results from the GPU 1212to the CPU 1211 after the arithmetic operation in the GPU 1212 can beperformed at high speed.

The analog arithmetic unit 1213 includes one or both of an A/D(analog/digital) converter circuit and a D/A (digital/analog) convertercircuit. Furthermore, the product-sum operation circuit may be providedin the analog arithmetic unit 1213.

The memory controller 1214 includes a circuit functioning as acontroller of the DRAM 1221 and a circuit functioning as an interface ofthe flash memory 1222.

The interface 1215 includes an interface circuit for an externalconnection device such as a display device, a speaker, a microphone, acamera, or a controller. Examples of the controller include a mouse, akeyboard, and a game controller. As such an interface, a USB (UniversalSerial Bus), an HDMI (registered trademark) (High-Definition MultimediaInterface), or the like can be used.

The network circuit 1216 includes a network circuit such as a LAN (LocalArea Network). The network circuit 1216 may further include a circuitfor network security.

The circuits (systems) can be formed in the chip 1200 through the samemanufacturing process. Therefore, even when the number of circuitsneeded for the chip 1200 increases, there is no need to increase thenumber of manufacturing processes; thus, the chip 1200 can be fabricatedat low cost.

The motherboard 1203 provided with the PCB 1201 on which the chip 1200including the GPU 1212 is mounted, the DRAMs 1221, and the flash memory1222 can be referred to as a GPU module 1204.

The GPU module 1204 includes the chip 1200 using SoC technology, andthus can have a small size. In addition, the GPU module 1204 isexcellent in image processing, and thus is suitably used in a portableelectronic device such as a smartphone, a tablet terminal, a laptop PC,or a portable (mobile) game machine. Furthermore, the product-sumoperation circuit using the GPU 1212 can execute arithmetic operation ina deep neural network (DNN), a convolutional neural network (CNN), arecurrent neural network (RNN), an autoencoder, a deep Boltzmann machine(DBM), a deep belief network (DBN), or the like; thus, the chip 1200 canbe used as an AI chip or the GPU module 1204 can be used as an AI systemmodule.

The structure described in this embodiment can be used in combinationwith the structures described in the other embodiments as appropriate.

Embodiment 5

In this embodiment, application examples of the memory device using thesemiconductor device described in the above embodiment will bedescribed. The semiconductor device described in the above embodimentcan be applied to, for example, memory devices of a variety ofelectronic devices (e.g., information terminals, computers, smartphones,e-book readers, digital cameras (including video cameras), videorecording/reproducing devices, and navigation systems). Here, thecomputers refer not only to tablet computers, notebook computers, anddesktop computers, but also to large computers such as server systems.Alternatively, the semiconductor device described in the aboveembodiment is applied to a variety of removable memory devices such asmemory cards (e.g., SD cards), USB memories, and SSDs (solid statedrives). FIG. 30 schematically illustrates some structure examples ofremovable memory devices. The semiconductor device described in theabove embodiment is processed into a packaged memory chip and used in avariety of storage devices and removable memories, for example.

FIG. 30(A) is a schematic diagram of a USB memory. A USB memory 1100includes a housing 1101, a cap 1102, a USB connector 1103, and asubstrate 1104. The substrate 1104 is held in the housing 1101. Thesubstrate 1104 is provided with a memory chip 1105 and a controller chip1106, for example. The semiconductor device described in the aboveembodiment can be incorporated in the memory chip 1105 or the like onthe substrate 1104.

FIG. 30(B) is an external schematic diagram of an SD card, and FIG.30(C) is a schematic diagram illustrating the internal structure of theSD card. An SD card 1110 includes a housing 1111, a connector 1112, anda substrate 1113. The substrate 1113 is held in the housing 1111. Thesubstrate 1113 is provided with a memory chip 1114 and a controller chip1115, for example. When the memory chip 1114 is also provided on theback side of the substrate 1113, the capacity of the SD card 1110 can beincreased. In addition, a wireless chip with a radio communicationfunction may be provided on the substrate 1113, in which case data canbe read from and written in the memory chip 1114 by radio communicationbetween a host device and the SD card 1110. The semiconductor devicedescribed in the above embodiment can be incorporated in the memory chip1114 or the like on the substrate 1113.

FIG. 30(D) is an external schematic diagram of an SSD, and FIG. 30(E) isa schematic diagram illustrating the internal structure of the SSD. AnSSD 1150 includes a housing 1151, a connector 1152, and a substrate1153. The substate 1153 is held in the housing 1151. The substrate 1153is provided with a memory chip 1154, a memory chip 1155, and acontroller chip 1156, for example. The memory chip 1155 is a work memoryof the controller chip 1156, and a DOSRAM chip can be used, for example.When the memory chip 1154 is also provided on the back side of thesubstrate 1153, the capacity of the SSD 1150 can be increased. Thesemiconductor device described in the above embodiment can beincorporated in the memory chip 1154 or the like on the substrate 1153.

This embodiment can be implemented in combination with any of thestructures described in the other embodiments and the like, asappropriate.

Embodiment 6

In this embodiment, a product image applicable to the semiconductordevice of one embodiment of the present invention and specific examplesof electronic devices will be described using FIG. 31 and FIG. 32.

First, FIG. 31 illustrates a product image applicable to thesemiconductor device of one embodiment of the present invention. Aregion 501 illustrated in FIG. 31 represents high temperaturecharacteristics (High T operate), a region 502 represents high frequencycharacteristics (High f operate), a region 503 represents low offcharacteristics (Ioff), and a region 504 represents a region where theregion 501, the region 502, and the region 503 overlap one another.

Note that when the region 501 is intended to be satisfied, it can beroughly satisfied by using a carbide or a nitride such as siliconcarbide or gallium nitride for a channel formation region of asemiconductor device. When intended to be satisfied, the region 502 canbe roughly satisfied by using a silicide such as single crystal siliconor crystalline silicon for a channel formation region of a semiconductordevice. In addition, when intended to be satisfied, the region 503 canbe roughly satisfied by using an oxide semiconductor or a metal oxidefor a channel formation region of a semiconductor device.

The semiconductor device of one embodiment of the present invention canbe favorably used for a product in the range represented by the region504, for example.

A conventional product has difficulty in satisfying all of the region501, the region 502, and the region 503. However, the semiconductordevice of one embodiment of the present invention includes a crystallineOS in a channel formation region. In the case where the crystalline OSis included in the channel formation region, a semiconductor device andan electronic device satisfying high temperature characteristics, highfrequency characteristics, and low off characteristics can be provided.

Note that examples of a product in the range represented by the region504 are an electronic device including a low-power consumption andhigh-performance CPU, an in-car electronic device required to have highreliability in a high-temperature environment, and the like.

More specifically, the semiconductor device of one embodiment of thepresent invention can be used for a chip or a processor such as a CPU ora GPU. FIG. 32 illustrates specific examples of electronic devicesincluding a chip or a processor such as a CPU or a GPU of one embodimentof the present invention.

<Electronic Device and System>

The GPU or the chip according to one embodiment of the present inventioncan be mounted on a variety of electronic devices. Examples ofelectronic devices include a digital camera, a digital video camera, adigital photo frame, a cellular phone, a portable game machine, aportable information terminal, and an audio reproducing device inaddition to electronic devices provided with comparatively largescreens, such as a television device, a desktop or laptop personalcomputer, a monitor for a computer or the like, digital signage, and alarge game machine like a pachinko machine. In addition, when anintegrated circuit or a chip according to one embodiment of the presentinvention is provided in the electronic device, the electronic devicecan include artificial intelligence.

The electronic device of one embodiment of the present invention mayinclude an antenna. When a signal is received by the antenna, theelectronic device can display a video, data, or the like on the displayportion. When the electronic device includes the antenna and a secondarybattery, the antenna may be used for contactless power transmission.

The electronic device of one embodiment of the present invention mayinclude a sensor (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature, achemical substance, sound, time, hardness, an electric field, current,voltage, power, radioactive rays, flow rate, humidity, a gradient,oscillation, odor, or infrared rays).

The electronic device of one embodiment of the present invention canhave a variety of functions. For example, the electronic device in thisembodiment can have a function of displaying a variety of data (a stillimage, a moving image, a text image, and the like) on the displayportion, a touch panel function, a function of displaying a calendar,date, time, and the like, a function of executing a variety of software(programs), a wireless communication function, and a function of readingout a program or data stored in a recording medium. FIG. 32 illustratesexamples of electronic devices.

[Mobile Phone]

FIG. 32A illustrates a mobile phone (smartphone) which is a type of aninformation terminal. An information terminal 5500 includes a housing5510 and a display portion 5511. As input interfaces, a touch panel isprovided in the display portion 5511 and a button is provided in thehousing 5510.

When the chip of one embodiment of the present invention is applied tothe information terminal 5500, the information terminal 5500 can executean application utilizing artificial intelligence. Examples of theapplication utilizing artificial intelligence include an application forrecognizing a conversation and displaying the content of theconversation on the display portion 5511; an application for recognizingletters, figures, and the like input to the touch panel of the displayportion 5511 by a user and displaying them on the display portion 5511;and an application for performing biometric authentication usingfingerprints, voice prints, or the like.

[Information Terminal]

FIG. 32(B) illustrates a desktop information terminal 5300. The desktopinformation terminal 5300 includes a main body 5301 of the informationterminal, a display 5302, and a keyboard 5303.

Like the information terminal 5500 described above, when the chip of oneembodiment of the present invention is applied to the desktopinformation terminal 5300, the desktop information terminal 5300 canexecute an application utilizing artificial intelligence. Examples ofthe application utilizing artificial intelligence include design-supportsoftware, text correction software, and software for automatic menugeneration. Furthermore, with use of the desktop information terminal5300, novel artificial intelligence can be developed.

Note that in the above description, as examples of the electronicdevices, a smartphone and a desktop information terminal are shown inFIGS. 32(A) and 32(B), respectively, however, the electronic devices canbe information terminals other than a smartphone and a desktopinformation terminal. Examples of an information terminal other than thesmartphone and the desktop information terminal include a PDA (PersonalDigital Assistant), a notebook information terminal, and a workstation.

[Household Appliance]

FIG. 32(C) illustrates an electric refrigerator-freezer 5800 as anexample of a household appliance. The electric refrigerator-freezer 5800includes a housing 5801, a refrigerator door 5802, a freezer door 5803,and the like.

When the chip of one embodiment of the present invention is applied tothe electric refrigerator-freezer 5800, the electricrefrigerator-freezer 5800 including artificial intelligence can beachieved. Utilizing the artificial intelligence enables the electricrefrigerator-freezer 5800 to have a function of automatically making amenu based on foods stored in the electric refrigerator-freezer 5800,expiration dates of the foods, or the like, a function of automaticallyadjusting temperature to be appropriate for the foods stored in theelectric refrigerator-freezer 5800, and the like.

Although the electric refrigerator-freezer is described in this exampleas a household appliance, examples of other household appliances includea vacuum cleaner, a microwave oven, an electric oven, a rice cooker, awater heater, an IH cooker, a water server, a heating-coolingcombination appliance such as an air conditioner, a washing machine, adrying machine, and an audio visual appliance.

[Game Machine]

FIG. 32(D) illustrates a portable game machine 5200 as an example of agame machine. The portable game machine includes a housing 5201, adisplay portion 5202, a button 5203, and the like.

When the GPU or the chip of one embodiment of the present invention isapplied to the portable game machine 5200, the portable game machine5200 with low power consumption can be achieved. Moreover, heatgeneration from a circuit can be reduced owing to low power consumption;thus, the influence of heat generation on the circuit, a peripheralcircuit, and a module can be reduced.

Furthermore, when the GPU or the chip of one embodiment of the presentinvention is applied to the portable game machine 5200, the portablegame machine 5200 including artificial intelligence can be achieved.

In general, the progress of a game, the actions and words of gamecharacters, and expressions of a phenomenon and the like occurring inthe game are determined by the program in the game; however, the use ofartificial intelligence in the portable game machine 5200 enablesexpressions not limited by the game program. For example, it becomespossible to change expressions such as questions posed by the player,the progress of the game, time, and actions and words of gamecharacters.

In addition, when a game requiring a plurality of players is played onthe portable game machine 5200, the artificial intelligence can create avirtual game player; thus, the game can be played alone with the gameplayer created by the artificial intelligence as an opponent.

Although the portable game machine is illustrated as an example of agame machine in FIG. 32(D), the game machine using the GPU or the chipof one embodiment of the present invention is not limited thereto.Examples of the game machine to which the GPU or the chip of oneembodiment of the present invention is applied include a home stationarygame machine, an arcade game machine installed in entertainmentfacilities (a game center, an amusement park, and the like), and athrowing machine for batting practice installed in sports facilities.

[Moving Vehicle]

The GPU or the chip of one embodiment of the present invention can beapplied to an automobile, which is a moving vehicle, and the peripheryof a driver's seat in the automobile.

FIG. 32(E1) illustrates an automobile 5700, which is an example of amoving vehicle, and FIG. 32(E2) is a diagram illustrating thesurroundings of a windshield inside the automobile. FIG. 32(E2)illustrates a display panel 5701, a display panel 5702, and a displaypanel 5703 that are attached to a dashboard and a display panel 5704that is attached to a pillar.

The display panel 5701 to the display panel 5703 can provide a varietyof kinds of information by displaying a speedometer, a tachometer,mileage, a fuel gauge, a gear state, air-condition setting, and thelike. In addition, the content, layout, or the like of the display onthe display panels can be changed as appropriate to suit the user'spreference, so that the design quality can be increased. The displaypanel 5701 to the display panel 5703 can also be used as lightingdevices.

The display panel 5704 can compensate for view obstructed by the pillar(a blind spot) by showing an image taken by an imaging device (notillustrated) provided for the automobile 5700. That is, displaying animage taken by the imaging device provided outside the automobile 5700leads to compensation for the blind spot and an increase in safety. Inaddition, displaying an image to compensate for a portion that cannot beseen makes it possible for the driver to confirm the safety morenaturally and comfortably. The display panel 5704 can also be used as alighting device.

Since the GPU or the chip of one embodiment of the present invention canbe applied to a component of artificial intelligence, the chip can beused for an automatic driving system of the automobile 5700, forexample. The chip can also be used for a navigation system, riskprediction, or the like. A structure may be employed in which thedisplay panel 5701 to the display panel 5704 display navigationinformation, risk prediction information, or the like.

Note that although an automobile is described above as an example of amoving vehicle, the moving vehicle is not limited to an automobile.Examples of the moving vehicle include a train, a monorail train, aship, and a flying vehicle (a helicopter, an unmanned aircraft (adrone), an airplane, and a rocket), and these moving vehicles can eachinclude a system utilizing artificial intelligence when the chip of oneembodiment of the present invention is applied to each of these movingvehicles.

[Broadcasting System]

The GPU or the chip of one embodiment of the present invention can beapplied to a broadcasting system.

FIG. 32(F) schematically illustrates data transmission in a broadcastingsystem. Specifically, FIG. 32(F) illustrates a path in which a radiowave (a broadcast signal) transmitted from a broadcast station 5680 isdelivered to a television receiver (TV) 5600 of each household. The TV5600 includes a receiving device (not illustrated), and the broadcastsignal received by an antenna 5650 is transmitted to the TV 5600 throughthe receiving device.

Although a UHF (Ultra High Frequency) antenna is illustrated as theantenna 5650 in FIG. 32(F), a BS/110° CS antenna, a CS antenna, or thelike can also be used as the antenna 5650.

A radio wave 5675A and a radio wave 5675B are broadcast signals forterrestrial broadcasting; a radio wave tower 5670 amplifies the receivedradio wave 5675A and transmits the radio wave 5675B. Each household canview terrestrial TV broadcasting on the TV 5600 by receiving the radiowave 5675B with the antenna 5650. Note that the broadcasting system isnot limited to the terrestrial broadcasting shown in FIG. 32(F) and maybe satellite broadcasting using an artificial satellite, databroadcasting using an optical line, or the like.

The broadcasting system may be a broadcasting system utilizingartificial intelligence by applying the chip of one embodiment of thepresent invention. When broadcast data is transmitted from the broadcaststation 5680 to the TV 5600 of each household, the broadcast data iscompressed by an encoder. When the antenna 5650 receives the compressedbroadcast data, the compressed broadcast data is decompressed by adecoder of the receiving device included in the TV 5600. With use ofartificial intelligence, for example, a display pattern included in animage to be displayed can be recognized in motion compensationprediction, which is one of the compression methods for the encoder. Inaddition, in-frame prediction or the like can also be performedutilizing artificial intelligence. Furthermore, for example, whenbroadcast data with low resolution is received and the broadcast data isdisplayed on the TV 5600 with high resolution, image interpolationprocessing such as upconversion can be performed in the broadcast datadecompression by the decoder.

The broadcasting system utilizing artificial intelligence is suitablefor ultra-high definition television (UHDTV: 4K, 8K) broadcasting, whichneeds a larger amount of broadcast data.

In addition, as an application of artificial intelligence in the TV5600, a recording device including artificial intelligence may beprovided in the TV 5600, for example. With such a structure, theartificial intelligence in the recording device can learn the user'spreference, so that TV programs that suit the user's preference can berecorded automatically.

The electronic devices, the functions of the electronic devices, theapplication examples of artificial intelligence, their effects, and thelike described in this embodiment can be combined as appropriate withthe description of another electronic device.

This embodiment can be implemented in combination with any of thestructures described in the other embodiments and the like, asappropriate.

REFERENCE NUMERALS

100: capacitor, 100 a: capacitor, 110: conductor, 110 a: conductor, 112:conductor, 114: insulator, 114 a: insulator, 114 b: insulator, 116:insulator, 120: conductor, 120 a: conductor, 130: insulator, 130 a:insulator, 140: insulator, 140 a: insulator, 140 b: insulator, 150:insulator, 152: conductor, 154: insulator, 156: insulator, 200:transistor, 200 a: transistor, 200 b: transistor, 205: conductor, 205 a:conductor, 205 b: conductor, 210: insulator, 212: insulator, 214:insulator, 216: insulator, 222: insulator, 224: insulator, 230: oxide,230 a: oxide, 230A: oxide film, 230 b: oxide, 230B: oxide film, 230 c:oxide, 230C: oxide film, 231 a: region, 231 b: region, 234: region, 240:conductor, 240 a: conductor, 240 b: conductor, 241: insulator, 241 a:insulator, 241 b: insulator, 242: conductor, 242 a: conductor, 242A:conductive film, 242 b: conductor, 242B: conductor layer, 243: oxide,243 a: oxide, 243A: oxide film, 243 b: oxide, 243B: oxide layer, 245:conductor, 246: conductor, 246 a: conductor, 246 b: conductor, 247:conductor, 247 a: conductor, 247 b: conductor, 250: insulator, 250A:insulating film, 260: conductor, 260 a: conductor, 260Aa: conductivefilm, 260Ab: conductive film, 260 b: conductor, 265: dummy film, 265A:dummy film, 272: insulator, 272A: insulating film, 273: insulator, 273A:insulating film, 274: insulator, 276: insulator, 280: insulator, 281:insulator, 282: insulator

What is claimed is:
 1. A semiconductor device comprising: a firstinsulator, a first conductor in an opening in the first insulator; afirst oxide over the first insulator; a second conductor over the firstoxide; and a third conductor over the second conductor; wherein thesecond conductor is in contact with a top surface of the first conductorand a bottom surface of the third conductor.
 2. The semiconductor deviceaccording to claim 1, further comprising a fourth conductor below thefirst oxide.
 3. The semiconductor device according to claim 1, furthercomprising a second insulator over the second conductor, wherein thesecond insulator is in contact with the top surface of the secondconductor and a side surface of the third conductor.
 4. Thesemiconductor device according to claim 3, further comprising a thirdinsulator over the second conductor, wherein the third insulator is incontact with a side surface of the second conductor and a side surfaceof the second insulator.
 5. A semiconductor device comprising: a firstinsulator, a first conductor in an opening in the first insulator; afirst oxide over the first insulator; a second conductor over the firstoxide; a third conductor over the second conductor; and a fourthconductor over the first oxide; wherein the second conductor is incontact with a top surface of the first conductor and a bottom surfaceof the third conductor, and wherein the fourth conductor does notoverlap with the second conductor.
 6. The semiconductor device accordingto claim 5, further comprising a fifth conductor below the first oxide.7. The semiconductor device according to claim 5, further comprising asecond insulator over the second conductor, wherein the second insulatoris in contact with the top surface of the second conductor and a sidesurface of the third conductor.
 8. The semiconductor device according toclaim 7, further comprising a third insulator over the second conductor,wherein the third insulator is in contact with a side surface of thesecond conductor and a side surface of the second insulator.